Neurodevelopmental toxicity in vitro: primary cell culture models for screening and risk assessment.

Robust models for the evaluation of developmental toxicity are briefly reviewed with emphasis on embryonic brain and retina cells in vitro. Organ slice and aggregate cultures under constant gyratory movement as well as high cell density monolayer ("micromass") cultures are considered as robust models. An in vitro model using high cell density monolayer and re-aggregated cells isolated from embryonic chick brain (ED 6) is presented. Cell development and differentiation of the astrocytes and nerve cells are monitored by marker proteins and cytotoxicity was quantified by neutral red uptake and protein content. Four human teratogens, six possible human teratogens and six unlikely human teratogens were tested in brain and retina cells for their cytotoxic and morphologic effect. All 16 substances were classified correctly except the neurotoxicants MPTP and MPP+, both of which are strong dopaminergic toxicants in vitro as well as in humans and are therefore proposed to be classified as human neuroteratogens. Preliminary data on the lowest effect levels of four potential neurotoxicants (cadmium chloride, Ara-C, Phenytoin, MPTP) in chick brain aggregate cultures correlate surprisingly well with known toxic human plasma levels. Further validation has to be undertaken to confirm these promising results. A battery of such robust in vitro models is proposed that could cover neurodevelopmental toxicity of drugs and chemicals for screening and risk assessment purposes.