Electrocardiographic study of rat fetuses exposed to ethylene glycol monomethyl ether (EGME)

The urinary metabolic profile of diethylene glycol methyl ether and triethylene glycol methyl ether in Sprague-Dawley rats and the role of the metabolite methoxyacetic acid in their toxicity

Ethylene glycol ethers are a well-known series of solvents and hydraulic fluids derived from the reaction of ethylene oxide and monoalcohols. Use of methanol as the alcohol results in a series of mono, di and triethylene glycol methyl ethers. The first in the series, monoethylene glycol methyl ether (EGME or 2-methoxyethanol) is well characterised and metabolises in vivo to methoxyacetic acid (MAA), a known reproductive toxicant. Metabolism data is not available for the di and triethylene glycol ethers (DEGME and TEGME respectively). This study evaluated the metabolism of these two substances in male rats following single oral gavage doses of 500, 1000 and 2000 mg/kg for DEGME and 1000 mg/kg for TEGME. As for EGME, the dominant metabolite of each was the acid metabolite derived by oxidation of the terminal hydroxyl group. Elimination of these metabolites was rapid, with half-lives <4 h for each one. Both substances were also found to produce small amounts of MAA (~0.5% for TEGME and ~1.1% for DEGME at doses of 1000 mg/kg) through cleavage of the ether groups in the molecules. These small amounts of MAA produced can explain the effects seen at high doses in reproductive studies using DEGME and TEGME.

A Computational Workflow for Probabilistic Quantitative in Vitro to in Vivo Extrapolation

A computational workflow was developed to facilitate the process of quantitative in vitro to in vivo extrapolation (QIVIVE), specifically the translation of in vitro concentration-response to in vivo dose-response relationships and subsequent derivation of a benchmark dose value (BMD). The workflow integrates physiologically based pharmacokinetic (PBPK) modeling; global sensitivity analysis (GSA), Approximate Bayesian Computation (ABC) and Markov Chain Monte Carlo (MCMC) simulation. For a given set of in vitro concentration and response data the algorithm returns the posterior distribution of the corresponding in vivo, population-based dose-response values, for a given route of exposure. The novel aspect of the workflow is a rigorous statistical framework for accommodating uncertainty in both the parameters of the PBPK model (both parameter uncertainty and population variability) and in the structure of the PBPK model itself recognizing that the model is an approximation to reality. Both these sources of uncertainty propagate through the workflow and are quantified within the posterior distribution of in vivo dose for a fixed representative in vitro concentration. To demonstrate this process and for comparative purposes a similar exercise to previously published work describing the kinetics of ethylene glycol monoethyl ether (EGME) and its embryotoxic metabolite methoxyacetic acid (MAA) in rats was undertaken. The computational algorithm can be used to extrapolate from in vitro data to any organism, including human. Ultimately, this process will be incorporated into a user-friendly, freely available modeling platform, currently under development, that will simplify the process of QIVIVE.

Use of Physiologically Based Kinetic Modeling-Based Reverse Dosimetry to Predict in Vivo Toxicity from in Vitro Data

The development of reliable nonanimal based testing strategies, such as in vitro bioassays, is the holy grail in current human safety testing of chemicals. However, the use of in vitro toxicity data in risk assessment is not straightforward. One of the main issues is that concentration-response curves from in vitro models need to be converted to in vivo dose-response curves. These dose-response curves are needed in toxicological risk assessment to obtain a point of departure to determine safe exposure levels for humans. Recent scientific developments enable this translation of in vitro concentration-response curves to in vivo dose-response curves using physiologically based kinetic (PBK) modeling-based reverse dosimetry. The present review provides an overview of the examples available in the literature on the prediction of in vivo toxicity using PBK modeling-based reverse dosimetry of in vitro toxicity data, showing that proofs-of-principle are available for toxicity end points ranging from developmental toxicity, nephrotoxicity, hepatotoxicity, and neurotoxicity to DNA adduct formation. This review also discusses the promises and pitfalls, and the future perspectives of the approach. Since proofs-of-principle available so far have been provided for the prediction of toxicity in experimental animals, future research should focus on the use of in vitro toxicity data obtained in human models to predict the human situation using human PBK models. This would facilitate human- instead of experimental animal-based approaches in risk assessment.

Birth defects in infants born to employees of a microelectronics and business machine manufacturing facility

BACKGROUND

Concerns about solvent releases from a microelectronics/business machine manufacturing facility in upstate New York led to interest in the health of former workers, including this investigation of birth defects in children of male and female employees.

METHODS

Children born 1983 to 2001 to facility employees were enumerated and matched to New York State's Congenital Malformations Registry. Reported structural birth defects were compared with numbers expected from state rates (excluding New York City), generating standardized prevalence ratios (SPRs). Exposure assessors classified employees as ever/never potentially exposed at the facility to metals, chlorinated hydrocarbons, and other hydrocarbons during windows critical to organogenesis (female workers) or spermatogenesis (male workers). Among workers, adjusted prevalence ratios were generated to evaluate associations between potential exposures and specific birth defects.

RESULTS

External comparisons for structural defects were at expectation for infants of male workers (SPR = 1.01; 95% confidence interval [CI], 0.77-1.29; n = 60) and lower for births to female workers (SPR = 0.84; 95% CI, 0.50-1.33; n = 18). Among full-term infants of male workers, ventricular septal defects (VSDs) were somewhat elevated compared with the general population (SPR = 1.58; 95% CI, 0.99-2.39; n = 22). Within the cohort, potential paternal metal exposure was associated with increased VSD risk (adjusted prevalence ratio = 2.70; 95% CI, = 1.09-6.67; n = 7).

CONCLUSION

While overall SPRs were near expectation, paternal exposure to metals (primarily lead) appeared to be associated with increased VSD risk in infants. Take-home of occupational exposures, nonoccupational exposures, and chance could not be ruled out as causes. Case numbers for many defects were small, limiting assessment of the role of occupational exposures. Birth Defects Research (Part A) 106:696-707, 2016. © 2016 Wiley Periodicals, Inc.

Toxicity review of ethylene glycol monomethyl ether and its acetate ester

Ethylene glycol monomethyl ether (EGME) and its acetate ester (EGMEA) are highly flammable, colorless, moderately volatile liquids with very good solubility properties. They are used in paints, lacquers, stains, inks and surface coatings, silk-screen printing, photographic and photo lithographic processes, for example, in the semiconductor industry, textile and leather finishing, production of food-contact plastics, and as an antiicing additive in hydraulic fluids and jet fuel. EGME and EGMEA are efficiently absorbed by inhalation as well as via dermal penetration. Dermal absorption may contribute substantially to the total uptake following skin contact with liquids or vapours containing EGME or EGMEA. EGMEA is rapidly converted to EGME in the body and the two substances are equally toxic in animals. Therefore, the two substances should be considered as equally hazardous to man. Effects on peripheral blood, testes, and sperm have been reported at occupational exposure levels ranging between 0.4 and 10 ppm EGME in air, and with additional, possibly substantial, dermal exposure. Severe malformations and disturbed hematopoiesis have been linked with exposure to EGME and EGMEA at unknown, probably high, levels. Embryonic deaths in monkeys and impaired spermatogenesis in rabbits have been reported after daily oral doses of 12 and 25 mg per kg body weight, respectively. In several studies, increased frequency of spontaneous abortions, disturbed menstrual cycle, and subfertility have been demonstrated in women working in the semiconductor industry. The contribution of EGME in relation to other exposure factors in the semiconductor industry is unclear.

Maternal-fetal electrocardiographic effects and pharmacokinetics after an acute i.v. administration of caffeine to the pregnant rat

The relationship between fetal exposure and cardiovascular functional effects in the caffeine-treated pregnant rat was investigated. Caffeine (100 mg/kg) was administered intravenously to dams on day 21 of gestation. The transplacental transport of caffeine was studied by obtaining maternal and fetal blood (umbilical vein) samples at designated times after drug administration. Concurrent maternal-fetal electrocardiograms (ECGs) were measured and evaluated for caffeine-induced changes. Maternal and fetal plasma caffeine levels as well as area under the curve values were proportionally related throughout the experiment, indicative of equal exposure to caffeine. The fetal ECG exhibited more extensive changes associated with caffeine than did the dam's, but the effects were not detected in the first 30 min, suggesting a lag period for the action of caffeine on the fetal heart. The frequency of fetal ectopic beats and abnormal T waves were directly related to fetal plasma caffeine levels. Fetal ECG combined with the fetal blood microsampling technique was a practical method of testing for prefunctional effects of caffeine in the rat fetus.

[Progress report. What can one expect from a "functional prenatal toxicology?"]

In the strategy of investigation applied and demanded in prenatal toxicology partial aspects have been overstressed until now, although here as well as in postnatal toxicology the problems should be viewed in its complexity (in this case, F1-generation in its several pre- and postnatal stages of development). Therefore, there was the urgent need to summarize the existing methods of functional investigation in the field of prenatal toxicology and to compare them with conventional morphological methods as to their meaningfulness and sensitivity. As a result, the routine introduction of clinical-functional investigations is demanded.

Effects of 2-methoxyethanol on fetal development, postnatal behavior, and embryonic intracellular pH of rats

The industrial solvent 2-methoxyethanol (2ME) is a reproductive and developmental toxicant when administered by inhalation, gavage, and IP injection. The present research established that this solvent can produce teratogenicity in rats when administered in liquid diet. Groups of 10 Sprague-Dawley rats were given various percentages of 2ME in liquid diet on gestation days 7-18. Day 20 fetuses were examined for visceral or skeletal malformations. Concentrations above 0.025% 2ME (approximately 73 mg/kg/day) produced total embryo-mortality. Cardiovascular malformations were produced at lower levels. The teratogenic no-effect level was 0.006% 2ME (16 mg/kg). In a second experiment, groups of 12 Sprague-Dawley rats were given 0, 0.006 and 0.012% of 2ME as above. Litters were culled to 8 pups, and tested for auditory and tactile startle and conditioned lick suppression, and for performance in figure-8 activity and the Cincinnati water maze on postnatal days 48-65. The high dose of 2ME produced approximately 50% mortality in the offspring and increased the number of errors in the Cincinnati maze. No other behavioral effects were observed at either dose. An interaction study was conducted to determine if simultaneous exposure to 2ME and ethanol would reduce the teratogenicity of 2ME, but no reduction was observed. The hypothesis that 2ME acts by altering embryonic intracellular pH was tested by injecting 0.33 ml/kg of 2ME into rats on gestation day 13, and determining embryonic intracellular pH at 2, 4, 8, and 24 hours thereafter. There was an increase in pH at 4 hours, but not at later time points. Another group of rats was given 2ME along with amiloride, which blocks the sodium/hydrogen antiporter. The combined 2ME-amiloride exposure produced an incidence of cardiovascular malformations in fetuses twice that of 2ME alone. These studies confirmed the structural teratogenicity of 2ME even when given in liquid diet, as it was given for the first time in the present study. At nonteratogenic doses, developmental toxicity (e.g., postnatal deaths) persisted, but only limited evidence of behavioral teratogenicity was observed. The pH data are consistent with the concept that 2ME may alter embryonic intracellular pH at critical stages of organogenesis.

Prenatal ethylene glycol monomethyl ether (EGME) exposure produces electrocardiographic changes in the rat

The purpose of the present study was to determine if electrocardiographic (EKG) changes observed in fetuses exposed in utero to ethylene glycol monomethyl ether (EGME) persisted beyond the fetal/neonatal period. Groups of pregnant Sprague-Dawley rats were gavaged on gestation days 7-13 (sperm = day 0) with 0, 50, or 75 mg/kg EGME. Body weight prior to delivery was reduced and gestation was prolonged in EGME-treated dams. EGME treatment reduced the percentage of pregnant dams that delivered, litter size, and pup weight. There were no survivors beyond 3 days of age in the 75 mg/kg EGME group. The number of litters surviving through weaning and weight gain of male and female offspring through 8 weeks of age were reduced in the 50 mg/kg EGME group. In this same group, heart weight was unaffected, but heart/body weight ratios were increased when rats were 8 weeks old. EKGs were obtained from unanesthetized and unrestrained rats at 3 and 6 weeks of age. Prenatal EGME exposure increased the QRS interval in 3- and 6-week-old rats, and increased the T wave in 6-week-old rats. Thirty-six and 54% of 3- and 6-week old litters, respectively, had one or more individuals that were classified as having an intraventricular conduction delay (double R wave and QRS interval of 14 msec or longer). No microscopic heart abnormalities were associated with the observed intraventricular conduction delay.

Calcium homeostasis in pregnant rats treated with ethylene glycol monomethyl ether (EGME)

The industrial solvent ethylene glycol monomethyl ether (EGME) is a known teratogen that has been reported to alter calcium metabolism in guinea pigs during chronic exposure. Because of the tremendous demand of reproduction on maternal calcium stores, the effects of EGME on calcium and vitamin D metabolism during gestation were examined. Timed pregnant rats were treated by gavage with 0, 50, or 100 mg/kg EGME in 10 ml/kg distilled water on Days 9-15 of gestation (sperm = Day 1) and examined on Days 16 and 21. Virgin rats were treated for 7 days with 0 or 100 mg/kg EGME and examined 5 days later. EGME exposure did not affect body or kidney weight in virgin or pregnant rats, but liver weight was reduced in near-term pregnant rats treated with 100 mg/kg EGME. EGME (50 mg/kg) reduced litter size and fetal body weight and caused a significant number of live fetuses to have visceral abnormalities. EGME (100 mg/kg) caused all fetuses to be resorbed. In nonpregnant rats, 100 mg/kg did not affect serum 1,25-dihydroxyvitamin D (1,25(OH)2D3), 25-hydroxyvitamin D, ionic calcium, total calcium, or parathyroid hormone. EGME appeared to have a dose-dependent effect on calcium and vitamin D metabolism during gestation. On Day 21 of gestation, total calcium and ionic calcium were increased and 1,25(OH)2D3 was reduced in rats treated with EGME compared with nontreated controls. However, significant alterations in calcium homeostasis were evident only in dams that completely resorbed their litters. The changes in calcium and vitamin D metabolism during gestation appear to be secondary to the EGME-induced loss of litters.

Ornithine decarboxylase activity in the neonatal rat heart following prenatal exposure to ethylene glycol monomethyl ether

In mammals, ornithine decarboxylase (ODC) activity is highest during periods of rapid cellular growth and development, and the normal pattern of ODC activity during this period is sensitive to chemical and drug exposure. The industrial solvent ethylene glycol monomethyl ether (EGME) is teratogenic to rats and mice, with the heart being particularly sensitive. Basal ODC activity and ODC activity following an isoproterenol challenge were used to assess heart function in 3-, 9-, 16- and 22-day-old offspring from dams treated with 25 mg/kg EGME by gavage on days 7-13 or 13-19 of gestation. Reproductive outcome was not affected by EGME and none of the offspring had gross physical abnormalities. Gestation length was prolonged by both EGME treatments, but the increase was statistically significant only in the group treated on days 7-13 gestation. ODC activity per mg protein was greatest in 3-day-old rats and dropped off sharply during the following 3 weeks. In 3-day-old rats exposed on days 7-13 of gestation, ODC activity was 54% of that found in controls. ODC activity was comparable to that in controls in 3-day-old rats exposed on days 13-19 of gestation. Isoproterenol increased ODC activity in all groups, but additional functional abnormalities were not revealed by the isoproterenol challenge.

Ethylene glycol monomethyl ether (EGME) inhibits rat embryo ornithine decarboxylase (ODC) activity

The effects of ethylene glycol monomethyl ether (EGME) on reproductive outcome in the rat, and on ornithine decarboxylase (ODC) activity in the rat embryo were evaluated. Dams (n = 8) were treated by gavage on gestation days 6-12 (sperm = day 0) with 0, 25, 50 or 75 mg/kg EGME in 10 ml/kg distilled water. EGME had a dose-dependent effect on reproductive outcome. Gestation length was prolonged, and the number of litters delivered and neonatal body weight were reduced. Whole embryo ODC was measured on gestation days 9, 11, 13 and 15. ODC attained maximum activity in controls on day 11, increasing by more than an order of magnitude above the activity found on day 9. On day 11, a statistically significant dose-dependent inhibition of ODC activity was observed with the maximum dose of EGME inhibiting ODC activity 60 percent. On days 13 and 15, ODC activity declined markedly from peak values, and the dose-dependent inhibition was no longer evident. The study demonstrates a correlation between the inhibition of embryonic ODC activity by EGME and the effect of EGME on reproductive outcome.