Developmental toxicity in rats of a hemoglobin-based oxygen carrier results from impeded function of the inverted visceral yolk sac

•Infusion HBOC into pregnant rats causes developmental toxicity.•Sensitive from GD 7 to 11 when inverted yolk sac placenta (invYSP) supplies nutrition.•Controls for protein content, oncotic properties and Hb show effects are due to Hb.•Whole embryo culture verified HBOC interference with invYSP function.•Humans lack invYSP and are unlikely to be affected by HBOC. HBOC-201 is a bovine-derived, cross-linked, and stabilized hemoglobin (250kDa) in physiological saline. Daily intravenous infusions of HBOC (1.95, 3.90, or 5.85g/kg/day) during gestational days (GDs) 6–18 in Sprague-Dawley rats caused fetal mortality, reduced birth weight, and malformations. Subsequent single-day infusions (5.85g/kg/day) showed that developmental toxicity was limited to GDs 7–9 when histiotrophic nutrition via the inverted visceral yolk sac (invVYS) is essential. Histiotrophic nutrition is receptor-mediated endocytosis of bulk maternal proteins and subsequent lysosomal degradation providing amino acids and other nutrients for embryonic growth. Controls for protein content, oncotic properties, and hemoglobin content indicated that toxicity was due to hemoglobin. Rat whole embryo cultures verified HBOC interference with invVYS transport capacity and resultant deficient embryonic nutrition. These mechanisms of action are not expected to impact human development based on differences in VYS morphology and function, although a complete understanding of early human embryonic nutrition is lacking.