Developmental Toxicology

Introduction

Different periods during development vary in their sensitivity to the induction of developmental toxicity. Exposure to chemicals (such as certain anti-epileptic drugs) during early development (embryogenesis) may for instance result in congenital malformations (the process of teratogenesis), whereas other toxicants act in a more subtle manner on brain development in animal models and have the potential to cause irreversible behavioral changes. Overall, individuals tend to be more sensitive to toxicity during early development than in adult age, with the additional prospect that early induced effects have a greater potential to span a whole lifetime.

Embryotoxicity and in vitro methods

Research that provides a better understanding of the mechanistics behind different types of developmental toxicity and improves in vitro toxicity methodology for the screening and/or lead optimization of potential developmental toxicants is clearly needed. Part of our research focuses on the embryogenesis period and emphasizes the developmental toxicity effects of anti-epileptic drugs on neural tube closure (alterations causing malformations such as spina bifida and anencephaly) and cardiovascular development. We are especially interested in the anti-epileptic drug Valproic acid (VPA, branded product names are Erginyl or Depakene). VPA has among its many interesting biological properties, the ability to influence epigenetic processes through histone deacetylase (HDAC) inhibition activity and thereby gene expression activity. To study this and other mechanistic properties, we use flow cytometry and/or microarrays to analyze the differences in global gene expression patterns after drug exposure in different cell systems (mouse and human embryonic stem cells, primary human placental cell cultures of pericytes).

At the same time, we use and aim to improve more complex in vitro toxicity methods such as the whole embryonic culture (WEC), with special focus on the technical (image analysis, culture conditions) and bioinformatical aspects (semantic networks and anatomical ontologies, data analysis methods). We are focusing among other things on developing a version of WEC for the toxicity testing for embryonic heart rate modulators.

Improved in vitro systems will hopefully help in the prediction of developmental toxicity properties of drug candidates, unknown/uncharacterized drugs and chemicals and reduce the cost and the large amount of animals needed for developmental toxicity testing today. This is especially relevant considering the requirement by the EU program REACH to test thousands of chemicals.

Developmental neurotoxicity

It is more difficult to design in vitro toxicity tests for subtle developmental toxicity effects such as neonatal exposure induced changes in behavior in adult age (mainly studied in birds and rodents). It is generally recognized that developmental exposure to numerous drugs and chemicals can affect brain development and cause transient or irreversible behavioral changes in model organisms. Considering that the nature of such tests precludes any easy comparison to human conditions, risk assessment of drugs and chemicals for this kind of developmental toxicity is therefore entirely dependent on model organisms. Is is therefore essential to gain a better understanding of the mechanisms behind developmental toxicity leading to behavioral alterations.

Our group investigates the initial gene and protein expression changes in animal models where developmental exposure results in enduring behavior alterations later in life. This regards both developmental endocrine disruption effects on adult sexual behavior (using avian models) and effects on spontaneous activity, learning and memory (using a mouse model, in vivo and in vitro). The neurotoxicity studies in mouse use BDE-99, a chemical that belongs to a specific class of brominated flame retardants that nowadays are common environmental pollutants, and whose levels are known to be elevated in human populations in Asia and North America. The microarray studies are complemented with gel-based proteomics (2D-DIGE coupled to mass spectrometry) and LC-MS to study protein expression changes, MALDI mass spectrometry imaging for spatial localization, and a peptidomics LC-MS approach to analyze neuropeptide expression. A better mechanistic understanding of this type of subtle, potentially long-term, neurotoxicity will hopefully help in making risk assessments regarding their (and other chemicals like them) potential impact on both human health and wildlife.

Principal investigator: Lennart Dencker