A dysmorphology score system for assessing embryo abnormalities in rat whole embryo culture.

BACKGROUND: The rodent whole embryo culture (WEC) system is a well-established model for characterizing developmental toxicity of test compounds and conducting mechanistic studies. Laboratories have taken various approaches in describing type and severity of developmental findings of organogenesis-stage rodent embryos, but the Brown and Fabro morphological score system is commonly used as a quantitative approach. The associated score criteria is based upon developmental stage and growth parameters, where a series of embryonic structures are assessed and assigned respective scores relative to their gestational stage, with a Total Morphological Score (TMS) assigned to the embryo. This score system is beneficial because it assesses a series of stage-specific anatomical landmarks, facilitating harmonized evaluation across laboratories. Although the TMS provides a quantitative approach to assess growth and determine developmental delay, it is limited to its ability to identify and/or delineate subtle or structure-specific abnormalities. Because of this, the TMS may not be sufficiently sensitive for identifying compounds that induce structure or organ-selective effects. METHOD: This study describes a distinct morphological score system called the "Dysmorphology Score System (DMS system)" that has been developed for assessing gestation day 11 (approximately 20-26 somite stage) rat embryos using numerical scores to differentiate normal from abnormal morphology and define the respective severity of dysmorphology of specific embryonic structures and organ systems. This method can also be used in scoring mouse embryos of the equivalent developmental stage. RESULT AND CONCLUSION: The DMS system enhances capabilities to rank-order compounds based upon teratogenic potency, conduct structure- relationships of chemicals, and develop statistical prediction models to support abbreviated developmental toxicity screens.

Development of a zebrafish embryo teratogenicity assay and quantitative prediction model.

BACKGROUND: A zebrafish (Danio rerio) teratogenicity assay has been developed and evaluated for its ability to predict the teratogenic potential of chemicals. METHODS: Zebrafish embryos were dechorionated and then exposed to a test solution from 4-6 hours post-fertilization, and embryos or larvae were assessed up to 5 days post-fertilization (dpf) for viability and morphology. In preliminary experiments, the potential time points for assessment of compound-induced dysmorphology and general toxicity parameters were evaluated, and 5 dpf was found to be the optimum developmental stage for evaluation. Additionally, a morphological scoring system was devised to identify the developmental no-observed-adverse-effect level (NOAEL). For assay evaluation, 34 compounds with adequate in vivo developmental toxicity data were chosen. The compound set represented diversity in teratogenic potencies, structural classes, and pharmacologic targets. For 31 test compounds, each was evaluated over a concentration range, while 3 others were insufficiently aqueous-soluble to be fully tested. For each of the 31 tested compounds, the 5 dpf NOAEL was determined, and the concentration resulting in 25% lethality (LC25) was calculated by curve-fitting. Teratogenic potential of each compound was predicted based on the ratio of the LC25 to the NOAEL. LC25/NOAEL ratios of 10 or greater were considered predictive of teratogenicity. RESULTS: The model successfully categorized 87% of the compounds as teratogens or non-teratogens, with only 2 false-positives (dimethyl phthalate and a Bristol-Myers Squibb (BMS) investigative compound) and 2 false-negatives (valproic acid and a BMS compound). CONCLUSIONS: The results indicate that this assay is promising for screening compounds for teratogenic potential. Birth Defects Res (Part B) 89:66-77, 2010. (c) 2010 Wiley-Liss, Inc.

Morphological score assignment guidelines for the dechorionated zebrafish teratogenicity assay.

BACKGROUND: Recently we reported the development and optimization of a zebrafish teratogenicity assay using dechorionated AB strain embryos, a promising assay that was 87% concordant in correctly identifying in vivo teratogens and non-teratogens from a set of 31 compounds (Brannen et al., 2010: Birth Defects Res 89:66-77). METHODS: This assay utilizes a zebrafish morphological score system to characterize adverse effects and identify the no-observed-adverse-effect level (NOAEL). RESULTS: This report describes in detail the morphological score system used in the dechorionated zebrafish embryo culture teratogenicity assay. The morphological assessment includes evaluation of most structures and organ systems and grades relative severity of abnormalities. CONCLUSIONS: To this end, the morphological score system provides information of tissue-specific teratogenicity that has been found to have good concordance with structures found affected in vivo and can also be used to rank compounds based on the severity of malformations.

Allogeneic murine pregnancy models for assessing the developmental effects of immune-stimulating antibodies: Challenges in reproducibility.

Literature suggests that murine allogeneic pregnancy models are an alternative approach for evaluating the developmental toxicity of immune-stimulating agents. In this study, multiple syngeneic and allogeneic murine pregnancy models were used to assess the potential embryo-fetal effects of four different murine antibodies (IgG1 or IgG2 ) that activate the immune system by binding to T-cell receptors (PD-L1, LAG-3, and GITR). The pregnancy models were generated by within and between matings of five different inbred strains of mice (CBA/CaJ, DBA/2J, BALB/c, C57BL/6, and CBA/J). The antibodies were administered every 2-3 days by intraperitoneal injection (n = 12-29/group) during gestation days 6 to 14. There were no differences in embryo-fetal endpoints between the allogeneic and syngeneic pregnancies. Additionally, treatment with the antibodies had no effect on mean postimplantation loss in either the syngeneic or allogeneic pregnancies despite confirmation of pharmacologically-relevant systemic exposures. These results suggest that allogeneic murine pregnancy models need further validation and testing before they can be reliably used as an alternative approach for assessing the developmental effects of agents that stimulate the immune system.