Effects of all-trans-retinoic acid and all-trans-retinoyl glucuronide in two in vitro systems of distinct biological complexity.
In vitro systems are widely used to evaluate the embryotoxic potential of retinoids. The effective concentrations of these retinoids, however, are not consistent in the various in vitro systems used in evaluating embryotoxicity. This may be explained by the different level of complexity for each individual system, which may lead to different concentrations of the substances in the target tissues. To verify this hypothesis we have compared two in vitro systems of distinct biological complexity: the rat whole embryo culture system, and the mouse limb bud organ culture system. The lipid soluble, teratogenic retinoid all-trans-retinoic acid (ATRA), and all-trans-retinoyl-beta-D-glucuronide (ATRAG), an endogenous, water-soluble and biologically active retinoid with limited placental transfer, were compared with regard to their embryotoxic potential in vitro. In both in vitro systems, ATRAG showed a lower degree of embryotoxicity than ATRA. In the limb bud organ culture, ATRAG revealed only slightly less toxicity than ATRA, whereas the effective concentrations of the two compounds in the whole embryo culture system differed by almost two orders of magnitude. During incubation with ATRAG, ATRA is generated by hydrolysis and is found in culture media and exposed tissues. The presence of membrane barriers around the developing embryo in the whole embryo culture system possibly prevents the transfer of ATRAG to the embryo and, therefore, its exposure to the active hydrolysis product ATRA. From these results we conclude that analysis of retinoid concentrations in the culture media and in the exposed tissues is essential for the interpretation of results obtained from in vitro toxicity testing.
Rühl
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Institut für Ernährungswissenschaft, Universität Potsdam, Potsdam Rehbrücke, Germany. rruehl@rz.uni-potsdam.de
Sass
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Nau
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Klug
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D000818:Animals; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000002:abnormalities / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D018878:Limb Buds / Q000002:abnormalities / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D013723:Teratogens / Q000493:pharmacokinetics / Q000633:toxicity*; D014212:Tretinoin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000633:toxicity*
D013723:Teratogens; C026787:retinoyl glucuronide; D014212:Tretinoin