The placental transfer and toxicity of selenite relative to cadmium in the human term perfused placenta

Abstract

Selenite and cadmium both cause reproductive effects in animals. Cadmium is an acute placental toxicant, with apparent limited transfer to the fetus. This study examines the placental transfer of selenite, and the hypothesis that similar to cadmium, selenite may also be a direct placental toxicant. Using dual perfusion of the human term placental lobule, both non-protein bound (< 776 Da) selenite and cadmium equilibrated across the placenta within 4 h. The transfer of selenium, added as selenite, was not limited at concentrations from 2-40 nmol/ml. At initial maternal concentrations of 20 nmol/ml, selenium attained higher concentrations in the fetal perfusate compared with cadmium concentrations. Protein binding of cadmium in perfusates (45 per cent at 30 min) and placental cytosol (approx. 87 per cent) was greater than selenium (perfusate, 7 per cent at 30 min, cytosol, 50-60 per cent), which may partially account for the differences in placental transfer. Cadmium (20 nmol/ml) produced adverse effects on the production and release of human chorionic gonadotropin (hCG) in 4 h. No adverse effects were noted during 4 h exposures to selenite at initial concentrations of up to 40 nmol/ml. Thus, unlike cadmium, in which placental accumulation and direct placental toxicity contributed to acute reproductive effects, selenite at concentrations up to 40 nmol/ml was not a direct toxicant under these perfusion conditions.