Developmental toxicity of ethylene glycol monopropyl ether in the rat

Triethylene Glycol Ethers: Evaluations of In Vitro Absorption Through Human Epidermis, 21-Day Dermal Toxicity in Rabbits, and a Developmental Toxicity Screen in Rats

The methyl, ethyl, and butyl ethers of triethylene glycol (TM, TE, and TB, respectively) were evaluated in three screening studies to assess their potential hazards to humans. The assessments included (1) an in vitro procedure to determine the ability of the materials to penetrate human skin, (2) a 21-day dermal limit test in rabbits to determine potential systemic toxicities, and (3) a screening procedure to evaluate the chemicals' potentials to induce developmental toxicity. In the in vitro dermal absorption procedure, the three test materials crossed human epidermis at molar rates 170-330 times more slowly than the lower molecular weight homolog ethylene glycol methyl ether (EM), a chemical known to induce systemic effects following skin application. In the 21-day dermal study, daily applications of 1000 mg/kg TM, TE, or TB did not produce systemic toxicity in male or female rabbits, including hematologic or testicular effects. The low dermal penetration rate of the triethylene glycol ethers may have played a role in this outcome. In the developmental toxicity screening test, oral doses of 1000 mg/kg given on Days 6-15 of gestation did not produce maternal toxicity in rats and had no effect on viability or growth of offspring, pre-or postnatally, indicating low developmental toxic potential for these compounds. The results of these studies indicate that triethylene glycol methyl, ethyl, and butyl ethers have very low capacities to be absorbed through the skin of exposed individuals, low potentials to produce systemic toxicity following oral or dermal exposures, and do not appear to be selectively toxic to the developing conceptus. The data clearly indicate that triethylene glycol ethers do not exhibit toxicologic profiles comparable to those of the methyl and ethyl ethers of ethylene glycol.

Assessing the toxic effects of ethylene glycol ethers using Quantitative Structure Toxicity Relationship models

Experimental determination of toxicity profiles consumes a great deal of time, money, and other resources. Consequently, businesses, societies, and regulators strive for reliable alternatives such as Quantitative Structure Toxicity Relationship (QSTR) models to fill gaps in toxicity profiles of compounds of concern to human health. The use of glycol ethers and their health effects have recently attracted the attention of international organizations such as the World Health Organization (WHO). The board members of Concise International Chemical Assessment Documents (CICAD) recently identified inadequate testing as well as gaps in toxicity profiles of ethylene glycol mono-n-alkyl ethers (EGEs). The CICAD board requested the ATSDR Computational Toxicology and Methods Development Laboratory to conduct QSTR assessments of certain specific toxicity endpoints for these chemicals. In order to evaluate the potential health effects of EGEs, CICAD proposed a critical QSTR analysis of the mutagenicity, carcinogenicity, and developmental effects of EGEs and other selected chemicals. We report here results of the application of QSTRs to assess rodent carcinogenicity, mutagenicity, and developmental toxicity of four EGEs: 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, and 2-butoxyethanol and their metabolites. Neither mutagenicity nor carcinogenicity is indicated for the parent compounds, but these compounds are predicted to be developmental toxicants. The predicted toxicity effects were subjected to reverse QSTR (rQSTR) analysis to identify structural attributes that may be the main drivers of the developmental toxicity potential of these compounds.

Supernumerary ribs in developmental toxicity bioassays and in human populations: incidence and biological significance

Supernumerary or accessory ribs (SNR), either lumbar (LR) or cervical (CR), are a common finding in standard developmental toxicology bioassays. The biological significance of these anomalies within the regulatory arena has been problematic and the subject of some debate. In rodents, the spontaneous incidence of SNR is species and strain related and ranges from <1% to >30%. Compound-induced LR are induced by a wide variety of chemical and physical agents when pregnant animals are exposed during specific gestational periods. A significant portion of the agent-induced LR may be due to maternal factors, as it has been shown that stress alone will induce LR in rodents. SNR are not isolated phenomena and signify basic alterations in the architecture of the axial skeleton. LR are associated with longer ribs, increased numbers of vertebrosternal ribs, and the presence of extra presacral vertebrae ("anteriorization"). CR are associated with reduced numbers of vertebrosternal ribs (posteriorization). It is evident that SNR are not a single anomaly, but consist of two unrelated structures: an extra rib that has a cartilaginous segment at the distal end, and an ossification site that lacks cartilage. These have a bimodal size distribution, with the population of extra ribs being significantly longer than the ossification sites, and 0.6 mm can be used as an approximate length for distinguishing the two populations in mice. Extra ribs are permanent structures in contrast to ossification sites that disappear postnatally, probably becoming part of the lateral transverse vertebral processes. SNR are also found in humans although, in contrast to laboratory species, CR are more commonly noted. SNR are associated with adverse heath effects, and CR with inducing thoracic outlet disease characterized by diminished blood flow and altered position of the ganglia and nerve roots in the area of the C7-T1 vertebrae. LR are associated with lower back pain and L4-5 degeneration. The incidence of CR is greatly reduced in adult humans as compared to fetuses, and it has been hypothesized that fetal "SNR" may be largely composed of ossification sites that disappear postnatally. The mechanisms involved in the formation of extra ribs are not understood at this time, although the fact that the early sensitive periods for their initiation during embryogenesis is coupled with the associated changes in the axial skeleton argues for their induction being due to fundamental changes in gene expression. The sum of the experimental evidence supports the idea of SNR being composed of two different structures: extra ribs that are permanent dysmorphological structures that may be induced by xenobiotics and/or maternal stress, and ossification sites that may be transient variations in the formation of the lateral processes of the vertebrae.

Embryotoxic and teratogenic effects of aluminum nitrate in rats upon oral administration

In order to determine the embryotoxic and teratogenic potential of aluminum, pregnant Sprague-Dawley rats were treated by gavage with a daily dose of 180, 360, or 720 mg/kg of aluminum nitrate from the sixth through to the fourteenth day of gestation. Fetal examinations were performed on day 20. The number of corpora lutea, total implants, and resorptions as well as the number of live and dead fetuses in the treated animals were not significantly different from the control group. Therefore, embryolethality of aluminum cannot be induced (as a measure of percent dead and resorbed fetuses). However, exposure of rats to aluminum nitrate resulted in decreased fetal body weight and increased the incidence and types of external, visceral, and skeletal malformations and variations in all the treated groups. Consequently, teratogenic effects of aluminum-nitrate administration may result in rats given high oral doses that induce concomitant maternal toxicity.

Teratology study of diethylene glycol mono-n-butyl ether in rats

The teratogenicity of diethylene glycol mono-n-butyl ether (DEGMBE) was studied in Wistar rats. The pregnant rats were fed a diet containing DEGMBE from day 0 through day 20 of pregnancy. The dietary concentrations of DEGMBE were 0, 0.04, 0.2 and 1% and the daily intakes of DEGMBE were 0, 25, 115 and 633 mg/kg, respectively. In the DEGMBE-treated groups, the maternal body weight gain during pregnancy was significantly reduced, but neither decrease in food consumption during pregnancy nor any clinical sign of toxicity was observed. No significant differences between the DEGMBE-treated groups and the control group were found in the pre- and postimplantation losses, the number of live fetuses per litter, the sex ratio of live fetuses, the fetal body weight and the placental weight. External, skeletal and internal examinations of the fetuses revealed no evidence of teratogenesis. In the postnatal development of the offspring from the dams given DEGMBE, a high survival rate and good growth of the offspring were noted. It could be concluded that DEGMBE has no adverse effects on the pre- and postnatal development of the offspring in rats.

A tier system for developmental toxicity evaluations based on considerations of exposure and effect relationships

The backlog of untested chemicals and the rate at which new substances enter the marketplace exceed our capacity for developmental effects testing by standard in vivo methods. However, conservative use of two observations in a manner consistent with present day understanding of abnormal developmental biology can more accurately focus attention and resources on those agents in greatest need of complex testing for effects on in utero development. These two observations are 1) most chemicals are no more toxic to embryonic development than they are to adult homeostasis and 2) most human exposure to chemicals is de minimus, i.e., so small that it is inconsequential. Recently devised in vitro assays to quantitatively rank chemicals according to their developmental hazard index, when used in conjunction with more conventional in vivo methods and appropriate considerations of exposure, permit evaluation of a significantly larger number of chemicals than is currently achieved. The methods described apply a tier approach to establish testing priorities that markedly reduce the time, cost, and number of laboratory animals needed for evaluation of developmental toxicity.