IDENTIFICATION OF PROXIMATE TOXICANT FOR ETHYLENE-GLYCOL DEVELOPMENTAL TOXICITY USING RAT WHOLE-EMBRYO CULTURE THE EFFECTS

The effects of ethylene glycol (EG) and its metabolite, glycolic acid (GA), were compared by culturing day 10.5 rat conceptuses for 46 h in media containing 0.5, 2.5, 12.5, 25 or 50 mM EG or GA. EG up to 50 mM was essentially without effect, whereas greater than or equal to 12.5 mM GA inhibited embryo growth and development. Craniofacial dysmorphog enesis was observed in 70% of the 12.5 mM GA embryos (0% in controls). To determine if GA toxicity in vitro was an indirect effect of medium acidification, embryos were cultured in 12.5 mM GA (pH 6.7), 12.5 mM sodium glycolate (pH 7.4), or in control medium (pH 7.4 or 6.7). The p ercentage of dysmorphic embryos was 67% for the 12.5 mM GA (pH 6.7) gr oup, 58% for the sodium glycolate (pH 7.4) group, 8% in the pH 6.7 con trols, and 0% in the pH 7.4 controls. These results suggest that GA, n ot parent EG, is the active toxicant for EG-induced developmental toxi city and that acidification of culture medium pH plays only a minor ro le in GA's effects in vitro. The identification of GA as the active to xicant is important for the risk assessment of EG because GA exhibits dose-rate-dependent, nonlinear kinetics in vivo. (C) 1996 Wiley-Liss, Inc.