Preliminary Results Using the Early Embryo Teratogenesis Assay: A Comparison of Early Embryo Abnormalities with Late Embryo and Hatchling Teratogenic Changes

Abstract

Classical evaluations of the effects of toxicants on development in birds for ecological impact assessments and teratogenic evaluation generally entail an evaluation of the late embryo, immediately before hatching, or young hatchling. In the laboratory, these studies generally require approximately three weeks before one can evaluate the late embryo or hatchling, and a full teratogenic evaluation of growth and developmental parameters is relatively time intensive. Recent studies have shown that many teratogenic abnormalities may be detected as soon as the affected organ system starts to develop or differentiate. The early embryo teratogenesis assay is being developed to reduce the amount of time needed to evaluate potential teratogenic or developmental toxicological effects. Embryos which have been exposed in the laboratory or in the natural environment are incubated (preferably in the laboratory) and sacrificed at known time points which correspond to the time when specific developmental indicators (such as the heart or visceral arches) have begun to develop. These embryos are then evaluated for the type and frequency of abnormalities manifested at each stage of development. We have begun a series of laboratory studies using both a laboratory model animal (the domestic chicken) and wildlife species (barn and tree swallows) which enable us to compare the early embryo abnormalities induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; chicken) or a mixture of environmental contaminants, which include TCDD-like compounds (swallow), to the abnormalities observed in the late embryo, hatchling or nestling.

Site Specific PCB-Correlated Interspecies Differences in Organ Somatic Indices

“…Later studies evaluating the effects of TCDD and PCBs on the development of embryonic hearts documented that the dose-responsive TCDD/PCB-induced heart abnormalities, like the brain abnormalities, are quantifiably detectable very early in embryonic development (Henshel et al, 1993). These characteristic heart abnormalities have been observed in tree swallow embryos from Winston-Thomas in a related part of our study (Henshel et al, 1997). Walker et al (1997) and Walker and Catron (2000) confirmed that approximately 60 ng/g TCDD toxic equivalents (TEQs) caused edema, structural changes, and increased heart weight due to dilation in developing chicken hearts by embryonic day 10 or 12.…”

External heart deformities in passerine birds exposed to environmental mixtures of polychlorinated biphenyls during development

“…Other studies evaluating the developmental effects of TCDD and PCBs on hearts have demonstrated that teratogenic changes are detectable as soon as the heart starts to form during embryonic development. Henshel [4,22] as well as Henshel et al [23] and Dickerson et al [37] showed that initial heart development was affected adversely by TCDD and that these delays and early heart malformations were observable at 2 and 10 pg TCDD/g egg (ϳ0.1 and 0.5 ng/egg), the lowest doses tested in each study. Walker et al [38] examined hearts from 10-d-old chicken embryos exposed to 1 pM TCDD per egg (0.54 ng of TCDD per 60-g egg; 9 ppt) from embryonic day 0 to embryonic day 10.…”

“…The heart is susceptible to dioxin and dioxin-like chemical exposure [6][7][8][22][23][24][25][26][27][28][29]. Previous work by our laboratory demonstrated that developmental TCDD exposure increased the incidence and severity of teratogenic heart deformities in chicken embryos [7,[22][23][24] exposed throughout the incubation period.…”

“…The heart is susceptible to dioxin and dioxin-like chemical exposure [6][7][8][22][23][24][25][26][27][28][29]. Previous work by our laboratory demonstrated that developmental TCDD exposure increased the incidence and severity of teratogenic heart deformities in chicken embryos [7,[22][23][24] exposed throughout the incubation period. Observed anomalies from these and other studies included increased heart weight [6,8], pericardial edema, cardiomyopathy [6,8,25], abnormal valve and vessel development [6], and decreased contractile response [25,28].…”