Relative potency of albendazole and its sulfoxide metabolite in two in vitro tests for developmental toxicity: the rat whole embryo culture and the mouse embryonic stem cell test.

The benzimidazole carbamate albendazole (ABZ), a potent anthelmintic, is a teratogenic compound in rats. At present it is unclear to which degree this effect is caused by the parent compound or its major metabolite, albendazole sulfoxide (ASO). Both substances were studied separately and in combinations to mimic incomplete bioactivation in two in vitro tests: mouse embryonic stem cell test (EST) and rat whole embryo culture (WEC). In both assays, ABZ and mixtures with ASO induced detrimental effects at lower concentrations compared to ASO alone. While ABZ caused half-maximal effects on cardiomyocyte differentiation at a mean concentration of 0.26 μM (EST) and dysmorphogenic development of rat embryos at 3.7 μM (WEC), effective concentrations of ASO were similar in both assays (10-13 μM). By using WEC and EST we demonstrate that ABZ exhibits stronger inherent embryotoxic potency although ASO might be the proximate teratogen in vivo because of higher plasma concentrations.