What are common agents causing developmental toxicity?
Thalidomide (limb defects), ethanol (fetal alcohol syndrome), valproic acid (neural tube defects), lead (cognitive deficits), retinoic acid (craniofacial defects).
What is the mechanism of thalidomide developmental toxicity?
[from slides] Many mechanisms of action for thalidomide-induced teratogenicity have been proposed, with oxidative stress receiving the most attention, but without consensus
Disrupts angiogenesis and redox signaling during limb development.
What is the mechanism of ethanol developmental toxicity? [not from slides]
Interferes with neural crest cell migration and differentiation.
What is the mechanism of valproic acid developmental toxicity?
Inhibits histone deacetylases (HDACs), altering gene expression during neural tube closure.
Antiepileptic drugs
A. Phenytoin, carbamazepine, valproic acid, and others
B. Can cause birth defects, cognitive impairment, and fetal death
C. The mechanism of teratogenicity is not known, but reactive metabolites and interference of folic acid metabolism, etc., have been suggested
What are biomarkers for developmental toxicity?
Reduced birth weight, skeletal anomalies (e.g., phocomelia), neurobehavioral deficits.
What are testing methods for developmental toxicity?
Segment II studies (embryo-fetal development), zebrafish assays (teratogenicity), in vitro embryotoxicity tests.
Summary of In Vivo Regulatory Protocol Guidelines for Evaluation of Developmental Toxicity
STUDY EXPOSURE ENDPOINTS COVERED COMMENTS
Segment I: ♂: 10 weeks prior to mating
♀: 2 weeks prior to mating Gamete development, fertility, pre- and postimplantation viability, parturition, lactation Assesses reproductive capabilities of ♂ and ♀ following exposure over one spermatogenic cycle or several estrous cycles
Segment II: Implantation (or mating) through end of organogenesis (or term) Viability and anatomy (external, visceral, skeletal) of fetuses prior to birth Shorter exposure prevents metabolic adaptation and provides high exposure during gastrulation and organogenesis. Earlier dosing option for bioaccumulative agents. Later dosing to cover reproductive tract development
Segment III: Last trimester of pregnancy through lactation Postnatal survival, growth, and external morphology To observe effects on development of major organ function during the perinatal period; may be more sensitive to adverse effects at this time
What are endpoints for developmental toxicity?
Structural malformations (e.g., cleft palate), functional deficits (e.g., learning disabilities), fetal death.
How does lead cause developmental toxicity? [not from slides]
Inhibits neuronal development and synaptic plasticity in the brain.
What is the role of retinoic acid in developmental toxicity? [not from slides]
Excess causes craniofacial defects via altered gene expression in neural crest cells.
How does ethanol affect fetal development?
Causes microcephaly and facial dysmorphia via oxidative stress and apoptosis.
