Embryolethality of new herbicides is not detected by the micromass teratogen tests

Effects of aliphatic nitriles in micromass cultures of rat embryo limb bud cells

The relative effects of a series of eight saturated (acetonitrile, propionitrile and n-butyronitrile) and unsaturated (acrylonitrile, allylnitrile, methacrylonitrile, cis-2-pentenenitrile, and 2-chloroacrylonitrile) aliphatic nitriles were evaluated using an in vitro test for embryotoxicity, the rat limb bud micromass assay. The concentrations that produced 50% inhibition (IC50) of viability and differentiation of the cultured embryonic cells were of the same order of magnitude, whatever tested compound. The IC50 values spread over a wide concentration range from 7-11 microM to 150 mM. Acetonitrile and 2-chloroacrylonitrile were the least and most potent compounds, respectively. The tested chemicals were evaluated using different criteria proposed to identify teratogens in the micromass system, based on either active concentrations or specific inhibition of cell differentiation. A few incorrect classifications were obtained with both nonteratogens and teratogens, when comparing the activity in limb bud cell cultures with the data available on their in vivo teratogenic potential in rats. The concordance between the in vitro and in vivo responses of this set of nitriles was judged insufficient to consider the micromass assay valuable for predicting the in vivo teratogenic outcome of this class of compounds.

The relative embryotoxicity of 1,3-dichloro-2-propanol on primary chick embryonic cells

1,3-Dichloro-2-propanol (1,3-DCP) is a chlorinated compound used in the fabrication of industrial products such as hard resins, celluloid or paints. It has also been detected in instant soups and soy sauce. 1,3-DCP has been associated with major necrosis of the liver in humans [Chem.-Bio. Interact. 80 (1991) 73]. In humans and laboratory animals, 1,3-DCP is metabolised to dichloroacetone (1,3-DCA) by cytochromes P450 2E1 and 1A2 [J. University Occup. Environ. Health 14 (1992) 13]. 1,3-DCA is a hepatotoxin. We suggest that 1,3-DCA could be embryotoxic at doses that do not cause adverse maternal hepatic damage. To investigate the embryotoxic effects of 1,3-DCA, we have adapted a micromass culture method from Atterwill and colleagues [1992. A tiered system for in vitro neurotoxicity testing. In: Zbinden, G. (Ed.), The Brain in Bits and Pieces. Verlag M.T.C., Vollikon, pp. 89-91], using chick midbrain cells and from Wiger et al. [Pharmacol. Toxicol. 62 (1988) 32] using chick mesenchymal cells. The basis of the micromass system is that embryotoxins in vitro are likely to affect development and differentiation of disaggregated neuronal and limb bud micromass cultures. The endpoints chosen for the midbrain assay are resazurin reduction (viability), total protein content (cell number), morphological quantification of neuronal cultures (neuronal projection number) and of limb bud cultures (cartilage nodule number). Preliminary results using chick whole embryo cultures indicated that 1,3-DCA had an inhibitory effect on whole chick embryo development. We also found that embryonic derived cells were sensitive to 1,3-DCA but not 1,3-DCP at concentrations above 1 microM, suggesting a potential teratogenic effect of 1,3-DCA. The exposure to 1,3-DCP is not limited to industrial settings, and hence a better knowledge of its effects and tissue specific actions on embryonic-derived cells would be beneficial.

A useful marker for evaluating tissue-engineered products: gap-junctional communication for assessment of the tumor-promoting action and disruption of cell differentiation in tissue-engineered products

An in vitro system for evaluating the safety of tissue-engineered products is a convenient because of its rapidity and low cost. On the basis of recent studies, intercellular channels called gap-junctions are considered to play an important role on the tumor-promotion stage during the tumorigenesis induced by polyurethanes. Further, we also demonstrate the significance of the intercellular communication during neuronal cell differentiation. From these results, we propose a survey of the function of the gap-junctional communication as a probable useful marker for evaluating the safety of tissue-engineered products.

Novel harmful effects of [60]fullerene on mouse embryos in vitro and in vivo

[60]Fullerene (C60) was solubilized with poly(vinylpyrrolidone) (PVP) in water, and the aqueous solution was applied to a mouse midbrain cell differentiation system. On incubation of C60 with various concentrations of PVP, cell differentiation and proliferation were potently inhibited, although weaker than the vehicle controls. C60 was clearly distributed into the yolk sac and embryos by intraperitoneal administration to pregnant mice at 50 mg/kg and had a harmful effect on both conceptuses by microscopical evaluation. This in vivo and in vitro action on embryogenesis is a novel and seriously harmful activity of C60.

In vitro tests for teratogens: desirable endpoints, test batteries and current status of the micromass teratogen test

Information from in vitro tests can be usefully used as a component of the risk/hazard assessment process. In vivo studies will be required to confirm the in vitro data. If the in vitro test system is designed around endpoints that reflect changes following in vivo toxic insult then it may be possible to modify the in vitro system to account for some of the discrepancies observed between in vivo and in vitro outcomes. When the discrepancy can be accounted for by low bioavailability in vivo, pharmacokinetic studies may be required to determine the relevance of the in vitro toxic concentrations. Reproductive hazard, especially teratogenicity, has been the subject of intensive in vitro test development. The observation of teratogenicity may affect the development of new products more significantly than any other type or category of reproductive toxicity. The micromass test, involving culture of differentiating rat embryo limb and midbrain cells exposed to test agents, may be useful as part of a battery of in vitro tests for teratogens. The most recent protocol for the micromass test is described, followed by a summary of validation and mechanistic studies confirming its usefulness. The test is robust in its transfer to new laboratories. Interlaboratory variability is small.