Teratogenicity of arotinoids (retinoids) in vivo and in vitro

Validation of the Rat Limb Bud Micromass Test in the International ECVAM Validation Study on Three In Vitro Embryotoxicity Tests

A detailed report is presented on the performance of the rat limb bud micromass (MM) test in a European Centre for the Evaluation of Alternative Methods (ECVAM)-sponsored formal validation study on three in vitro tests for embryotoxicity. Twenty coded test chemicals, classified as non-embryotoxic, weakly embryotoxic or strongly embryotoxic on the basis of their in vivo effects on animals and/or humans, were tested in four laboratories. The outcome showed that the MM test is an experimentally validated test, which holds promise for use for identifying strongly embryotoxic chemicals, but which needs to be improved before it can be recommended for use for regulatory purposes.

IFT80 is essential for chondrocyte differentiation by regulating Hedgehog and Wnt signaling pathways

Partial mutation of intraflagellar transport 80 (IFT80) in humans causes Jeune asphyxiating thoracic dystrophy (JATD) and short-rib polydactyly (SRP) syndrome type III. These diseases are autosomal recessive chondrodysplasias that share clinical similarities, including shortened long bones and constricted thoracic cage. However, the role and mechanism of IFT80 in the regulation of chondrocyte differentiation and function remain largely unknown. We hypothesize that IFT80 is required for the formation and function of cilia and plays a critical role in chondrogenic differentiation by regulating Hedgehog (Hh) and Wingless (Wnt) signaling pathways. To test this hypothesis, we first analyzed the IFT80 expression pattern and found that IFT80 was predominantly expressed in growth plate chondrocytes and during chondrogenic differentiation. Silencing IFT80 impaired cilia formation and chondrogenic differentiation in mouse bone marrow derived stromal cells (BMSCs), and decreased the expression of chondrocyte marker genes--collagen II and aggrecan. Additionally, silencing IFT80 down-regulated Hh signaling activity whereas up-regulated Wnt signaling activity. The overexpression of Gli2 in IFT80-silenced cells promoted chondrogenesis and recovered the chondrogenic deficiency from IFT80 silencing. Overall, our results demonstrate that IFT80 is essential for chondrocyte differentiation by regulating the Hh and Wnt signaling pathways.

In vitro culture of human chondrocytes (1): A novel enhancement action of ferrous sulfate on the differentiation of human chondrocytes

Chondrogenic differentiation of mesenchymal cells is generally thought to be initiated by the inductive action of specific growth factors and depends on intimate cell-cell interactions. The aim of our investigation was to characterize the influences of basic fibroblast growth factor (bFGF) and ferroussulfate (FeSO(4)) on proliferation and differentiation of human articular chondrocytes (HAC). This is the first report of the effects of FeSO(4) on chondrogenesis of HAC. Multiplied chondrocytes of hip and shoulder joints were cultured in chondrocyte growth medium supplemented with bFGF, FeSO(4), or both bFGF + FeSO(4) for4weeks. A 20 mul aliquot of a cell suspension containing2 x 10(7) cells ml(-1) was delivered onto each well of 24-well tissue culture plates. Cells cultured with the growth medium only was used as a control. Alamar blue and alcian blue staining were done to determine the chondrocyte proliferation and differentiation, respectively, after 4 weeks. The samples exposed to bFGF, FeSO(4), and combination of both indicated sufficient cell proliferation similar to the control level. Differentiations of the HAC exposed to bFGF, FeSO(4),and bFGF + FeSO(4) were 1.2-, 2.0-, and 2.2-fold of the control, respectively. Therefore, chondrocyte differentiation was significantly enhanced by the addition of FeSO(4) andbFGF + FeSO(4). The combined effects of bFGF and FeSO(4) were additive, rather than synergistic. These results suggest that treatment with ferrous sulfate alone or in combination with basic fibroblast growth factor etc, is a powerful tool to promote the differentiation of HAC for the clinical application.

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.

Characterization of synthetic retinoids with selectivity for retinoic acid or retinoid X nuclear receptors

The broad spectrum of physiological activities of retinoids is mediate d by two types of receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). Though they have 9-cis retinoic acid as a common ligand, the amino acid sequence of their ligand binding domains is only distantly related (27%). This fact makes it probable that the ligand binding pockets of RARs and RXRs differ significantly with respect to their three dimensional structure. Therefore, one can expect that selective ligands for these receptor subclasses do exit. A clear example of a naturally existing RAR-selective retinoid is all-trans retinoic acid. Here we report on two synthetic retinoids which are very closely related to retinoic acid in structure yet show good receptor subclass selectivity. These compounds have a saturated double bond in the polyene side chain between either the 7, 8 or 9, 10 carbon atoms and are highly RAR or RXR selective, respectively (as shown by receptor binding, transactivation activity and the ability to induce RXR homodimer formation). In addition, we present compounds of the synthetic arotinoid class which are highly RAR selective. Interestingly the corresponding '9-cis analogs' are not able to bind or activate RXR alpha and show greatly reduced activity on the RARs.

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.

Teratogenicity of arotinoids (retinoids) in the rat whole embryo culture

Structural modifications of the arotinoid molecule RO 13-7410 led to a difference in the teratogenic potencies of more than five orders of magnitude in mice in vivo and in micromass cultures of rat embryonic limb bud cells (Kistler et al. 1990). Five of these retinoids were selected and tested in rat whole embryo culture to determine the suitability of this in vitro test system for the identification of potentially non-teratogenic derivatives among this class of chemicals. The highest concentrations of the compounds with no effects (NOAEL) on general conceptus growth, on differentiation and on the frequency of dysmorphogenic embryos in vitro were compared with the lowest effective teratogenic doses in vivo (LOAEL) or with the concentrations leading to 50% inhibition of limb bud cell differentiation (IC50) in vitro. NOAEL's for the parameters of conceptus development ranged from 10(-5) micrograms/ml (0.03 nM) to 10 micrograms/ml (28.7 microM) for the compounds tested. These correlated very well with LOAEL and IC50 (R greater than 0.95). The types of dysmorphogenesis in vitro were those typical for retinoids, and for the most part resembled the malformations found in vivo. We conclude that the whole embryo culture system is a useful tool for the preliminary testing of retinoids.