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  • Title: Modulation of the embryotoxicity and cytotoxicity elicited by 7-hydroxy-2-acetylaminofluorene and acetaminophen via deacetylation.
    Author: Stark KL, Harris C, Juchau MR.
    Journal: Toxicol Appl Pharmacol; 1989 Mar 01; 97(3):548-60. PubMed ID: 2609350.
    Abstract:
    Acetaminophen (APAP) and 7-hydroxy-2-acetylaminofluorene (7-OH-AAF) each produced a similar incidence of, as well as a qualitatively similar, abnormal closure of the anterior neuropore at similar concentrations when added to the medium of cultured rat embryos. At concentrations producing a 50-65% incidence of abnormal neurulation, the affected embryos displayed relatively complete embryonic development as assessed from measurements of protein, axial rotation, and embryonic length. The neural tube defect produced by these agents consisted of elevated neural folds remaining separated by approximately 45 degrees as well as the presence of a mitotically active neural epithelium. In contrast, the nonacetylated structures, p-aminophenol (PAP) and 7-hydroxyaminofluorene (7-OH-AF), were embryotoxic at concentrations 10-fold lower than the corresponding acetylated compounds; each produced a greater incidence of abnormal axial rotation and a greater decrease in embryonic protein than APAP or 7-OH-AAF. In addition, the embryos exposed to PAP or 7-OH-AF were morphologically and histologically dissimilar to those exposed to the acetylated compounds. The neural folds of the latter remained elevated and in apposition, but lacked complete fusion of the folds of neural epithelium and were accompanied by marked cytotoxicity. Addition of active deacetylase sources (guinea pig liver microsomes or commercially obtained, purified carboxylic-ester hydrolase) to the culture medium of conceptuses exposed to 7-OH-AAF or APAP resulted in an increased embryotoxicity which was indistinguishable from that produced by the nonacetylated compounds alone. The increases in toxicity were effectively blocked by the addition of paraoxon, indicating that catalysis of the deacetylation of APAP and 7-OH-AAF was the causative factor. No evidence could be found for deacetylation of 7-OH-AAF or APAP mediated by the Day 10 conceptus itself. When examined for cytotoxicity in F9 embryonal carcinoma cells, APAP and 7-OH-AAF each produced observable cell death only if reduced glutathione (GSH) had previously been depleted and if a deacetylase source were present; this cytotoxicity was also blocked by addition of paraoxon. The nonacetylated metabolites were directly cytotoxic, although GSH depletion greatly increased the incidence of cell death. Therefore, deacetylation of APAP and 7-OH-AAF produced an increase in generalized embryotoxicity and cytotoxicity relative to abnormal neurulation, suggesting that APAP and 7-OH-AAF are capable of eliciting neural tube defects via a mechanism(s) that is distinguishable from the generalized embryotoxicity or cytotoxicity produced by their nonacetylated counterparts.
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