Dimethylaminoethanol is a close structural analog of choline, an essential nutrient. Dietary supplements containing dimethylaminoethanol bitartrate, a salt of dimethylaminoethanol, are marketed to improve memory and general cognitive function due to the ability of dimethylaminoethanol to increase levels of acetylcholine in the brain. Human exposure to dimethylaminoethanol may also occur through occupational and industrial routes (e.g., spray painting, beverage can lacquering, etc.). Dimethylaminoethanol was nominated by the National Institute of Environmental Health Sciences (NIEHS) for toxicologic characterization due to concerns for widespread human exposure through its use in industrial and consumer products. Due to limited literature indicating that dimethylaminoethanol may be a teratogen and reproductive toxicant and the possibility for widespread exposure to the salt form of dimethylaminoethanol (dimethylaminoethanol bitartrate) as a dietary supplement in women of childbearing age, the National Toxicology Program (NTP) conducted prenatal developmental toxicology studies in Sprague Dawley (Hsd:Sprague Dawley SD) rats. In these studies, time-mated female rats received dimethylaminoethanol bitartrate in sterile water by gavage from implantation on gestation day (GD) 6 to the day before expected parturition (GD 20). In order to identify dose levels that would appropriately challenge the model system, dimethylaminoethanol bitartrate-related maternal and fetal toxicity was examined in the dose range-finding study followed by the prenatal developmental toxicity study.
Dose Range-Finding Prenatal Developmental Toxicity Study
Groups of 10 time-mated female rats were administered 0, 250, 500, or 1,000 mg dimethylaminoethanol bitartrate/kg body weight per day in sterile water by gavage from GD 6 to GD 20. Vehicle control (0 mg/kg) animals received sterile water.
There were no indications of maternal or fetal toxicity in the dose range-finding study. All animals survived to study termination. There were no dose-related effects on maternal body weights, body weight gains, body weights corrected for live litter size, or feed consumption. The number of pregnant animals, mean number of corpora lutea, dead fetuses, early and late resorptions, and fetal sex ratio were similar across all treatment groups. There was a significant positive trend in the mean number of live female fetuses per litter relative to dose. There were no exposure-related fetal findings.
Prenatal Developmental Toxicity Study
As no maternal toxicity was observed in the dose range-finding study, groups of 25 time-mated female rats were administered 0, 250, 500, or 1,000 mg dimethylaminoethanol bitartrate/kg body weight per day in sterile water by gavage from GD 6 to GD 20. Vehicle control (0 mg/kg) animals received sterile water. In this study, dimethylaminoethanol bitartrate was well-tolerated and there were no significant effects on mortality, maternal body weights, body weight gains, body weights corrected for litter size, or feed consumption during gestation. One dam each in the 1,000 mg/kg group was euthanized moribund (GD 21) or found dead (GD 10), but these deaths were not considered dose-related. Clinical observations were limited to single or sporadic incidences with the exception of brown or red vaginal discharge, which was observed between GD 14 and GD 21 in 10/20, 3/20, 4/20, and 10/24 dams in the 0, 250, 500, and 1,000 mg/kg groups, respectively. There were no notable placental or other maternal gross observations at necropsy with the exception of a significant, but not biologically relevant, positive trend in mean absolute liver weight.
The number of pregnant animals, mean number of corpora lutea, implantations, litter size, live fetuses per litter, and fetal sex ratio were similar across all treatment groups.
External and visceral malformations were limited to common background findings and singular or sporadic incidences. There were no observed incidences of fetal head, specifically brain, abnormalities. Skeletal malformations and variations occurred predominantly in the ribs. A significant increase in the incidence of total, short thoracolumbar ribs (a variation) was observed in the 1,000 mg/kg group, along with a significant positive trend. Additionally, there was a significant increase in the number of supernumerary sites, or ossification sites, in the skull in 1,000 mg/kg fetuses as well as a significant positive trend across all groups. These effects may be reversible (supernumerary ribs) or of uncertain biological significance (supernumerary sites in the skull); however, in the absence of maternal toxicity or effects on fetal body weight, the increased incidences of extra ossification sites in two separate locations, each occurring through two different skeletal developmental pathways, suggest that these effects may be related to dimethylaminoethanol bitartrate exposure.