Abnormal neurulation induced by 7-hydroxy-2-acetylaminofluorene and acetaminophen: evidence for catechol metabolites as proximate dysmorphogens.
Direct additions to culture media of either acetaminophen (APAP) or 7-hydroxy-2-acetylaminofluorene (7-OH-AAF) resulted in abnormal closure of the anterior neuropores of cultured rat embryos in the absence of an exogenous bioactivation system. Concentrations required to produce a 50% incidence of the defect were approximately 500 and 250 microM for APAP and 7-OH-AAF, respectively. Losses of viability were not evident at these concentrations but 7-OH-AAF elicited a somewhat greater effect on growth parameters and generalized embryotoxicity. Transplacental induction with 3-methylcholanthrene (MC) of P450IA1 in subsequently cultured rat embryos did not detectably alter the capacity of APAP or 7-OH-AAF to effect embryotoxicity or neuropore closure. However, additions to the culture medium of exogenous hepatic bioactivating systems (S9) from MC-induced vs phenobarbital (PB)-induced adult rats produced profoundly different effects on neuropore closure. Coincubation with S9 from MC-induced rats reduced the incidence of 7-OH-AAF-elicited abnormal neuropores from 45 to 19%, whereas coincubation with S9 from PB-induced rats increased the incidence to 77%. Coincubation with MC-induced S9 produced no statistically significant effect on APAP-elicited neuropore abnormalities but, with PB-induced S9, resulted in a significant increase from 60 to 86%. Additions of 3-OH-APAP (0.1-0.2 mM) but not N-acetyl-p-benzoquinoneimine (NAPQI, 0.1-0.5 mM) to the culture medium elicited the typical neuropore abnormality. Experiments with APAP and 7-OH-AAF as substrates demonstrated that embryonic enzymes catalyzed their conversion to the corresponding catechols. Considered together, the results provided evidence that embryonic conversion of APAP or 7-OH-AAF to the corresponding catechol metabolites may be instrumental in effecting the abnormal anterior neuropore closure observed after exposure of embryos to the respective parent compounds.
Harris
C
C
Department of Pharmacology, School of Medicine, University of Washington, Seattle 98195.
Stark
K L
KL
Luchtel
D L
DL
Juchau
M R
MR
D015073:2-Acetylaminofluorene; D000014:Abnormalities, Drug-Induced / Q000378:metabolism*; D000082:Acetaminophen / Q000633:toxicity*; D000818:Animals; D001682:Biological Availability; D002396:Catechols / Q000378:metabolism*; D004247:DNA / Q000032:analysis; D004622:Embryo, Mammalian / Q000187:drug effects / Q000648:ultrastructure; D004790:Enzyme Induction; D006881:Hydroxyacetylaminofluorene / Q000633:toxicity*; D008658:Inactivation, Metabolic; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008748:Methylcholanthrene / Q000494:pharmacology; D009436:Neural Tube Defects / Q000139:chemically induced* / Q000378:metabolism; D009924:Organ Culture Techniques; D011506:Proteins / Q000032:analysis; D051381:Rats
D002396:Catechols; D011506:Proteins; D000082:Acetaminophen; D006881:Hydroxyacetylaminofluorene; D008748:Methylcholanthrene; D004247:DNA; D015073:2-Acetylaminofluorene