In vitro metabolism of teratogens by differentiating rat embryo cells.
Rapid and accurate prediction of teratogenic hazard had been achieved using cultures of differentiating limb mesenchyme (LB) and midbrain (CNS) cells from 13-day-old rat embryos. In this study we have used these cultures to examine the role of metabolism in the in vitro teratogenic activity of diphenylhydantoin (DPH) and cyclophosphamide (CPA). Two approaches were used. The first involved modulation of cytochrome P-450 activity by co-incubation in vitro with a variety of inhibitors at concentrations that were non-cytotoxic to the cells. This enhanced the toxicity of DPH by 13-82% in LB and by 3-52% in CNS cells. Benzimidazole and ellipticine caused the greatest enhancement and SKF 525A the least. DPH appears to be the proximate teratogen and there appear to be embryo-tissue cytochrome P-450s that assist in its detoxification. Following prior transplacental induction, CPA was toxic in vitro to LB cells from beta-naphthoflavone-pretreated mothers. CPA was non-toxic in cells of control, phenobarbitone- or 3-methylcholanthrene-treated embryos. Thus there appear to be inducible levels of cytochrome P-448 in embryo cells. In the second approach, positive immunocytochemical staining of the cells with both monoclonal and polyclonal P-450 antibodies identified phenobarbitone, beta-naphthoflavone- and 3-methylcholanthrene-inducible cytochrome P-450s at a constitutive level. Cytochromes P-448 (beta-naphthoflavone type) and P-450 (phenobarbitone type, PB3 fraction) were inducible, confirming that cytochrome P-450s are in fact present in the embryo cells.
D000818:Animals; D002478:Cells, Cultured; D019388:Cytochrome P-450 CYP1A2; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis; D003580:Cytochromes / Q000032:analysis; D004622:Embryo, Mammalian / Q000378:metabolism*; D005260:Female; D007527:Isoenzymes / Q000032:analysis; D010672:Phenytoin / Q000378:metabolism* / Q000633:toxicity; D051381:Rats; D013723:Teratogens / Q000378:metabolism*
D003580:Cytochromes; D007527:Isoenzymes; D013723:Teratogens; D010672:Phenytoin; D003577:Cytochrome P-450 Enzyme System; C017170:Cyp1a2 protein, rat; D019388:Cytochrome P-450 CYP1A2