nitrophenols and 2-aminofluorene

Placental biotransformation reactions may modulate the effect a xenobiotic has on the developing fetus. However, in spite of the critical role the placenta plays in supporting fetal life, little is known about the pharmacology and toxicology of the human placenta. Our laboratory has previously characterized the N-acetylation activity of the human term placenta. This activity is predominantly attributable to the NAT1 form of arylamine N-acetyltransferase (NAT). Although acetylation is generally thought to be a detoxifying reaction, both N-acetylation and deacetylation reactions play an important role in the activation of carcinogenic arylamines to their reactive and toxic forms. In the current study we characterized the activity of human placental NAT and deacetylase toward the carcinogenic arylamine, 2-aminofluorene (AF) and its acetylated metabolite, 2-acetylaminofluorene (AAF). 2-Aminofluorene is a synthetic, prototype carcinogenic arylamine compound, and its metabolism has been extensively studied in the laboratory. Our data show that the affinity (Km = 24.2 +/- 1.66 mumol/L; mean +/- SEM, n = 6) and maximal velocity (Vmax = 4.29 +/- 0.33 nmol/min/mg; mean +/- SEM, n = 6) of AF N-acetylation by human placenta are similar to those in human liver. The deacetylation of AAF to AF by placental microsomes may be catalyzed by a carboxylesterase. However, our studies with inhibitors reveal that the characteristics of human placental deacetylation activity differ from that of human liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 2-Acetylaminofluorene; Acetylation; Biotransformation; Carcinogens; Female; Fluorenes; Humans; Isocyanates; Microsomes, Liver; Nitrophenols; Placenta; Pregnancy

Dog urinary bladder is a target organ of carcinogenic arylamines. However, dog hepatic and urothelial cytosols lack acetylation enzymes that are capable of activating N-hydroxy metabolites of arylamines, suggesting that other enzymes may be involved. In the present study, we found that dog liver microsomes were capable of N-acetylation of 2-aminofluorene and N,O-acetyltransfer of N-hydroxy-2-acetylaminofluorene (N-OH-AAF), and that these activities were inhibited by paraoxon. The 0.25% Triton X-100 extractable fraction of microsomes was resolved on an ion-exchange column into three different proteins that retained these activities. Two of these proteins, designated as enzyme I and enzyme II, were further chromatographed on a Sephacryl S-300 column. As judged from the gel filtration profile, the mol. wt of enzyme I was approximately 180 kDa and that of enzyme II was greater than 700 kDa. SDS-PAGE analysis showed that the subunit weight of enzyme II was approximately 150 kDa. In addition to N-acetylation of 2-aminofluorene and N,O-acetyltransfer of N-OH-AAF, these three enzymes were capable of the deacetylation of 2-acetylaminofluorene, N-OH-AAF and 4-nitrophenyl acetate. The ability of these microsomal enzymes to activate N-hydroxylated aromatic amines and the presence of these enzymes in urothelial cells, reported previously, suggests that they may play an etiological role in the carcinogenicity of these agents in the dog.

Topics: 2-Acetylaminofluorene; Acetylation; Acetyltransferases; Acyltransferases; Amidohydrolases; Animals; Arylamine N-Acetyltransferase; Carcinogens; Chromatography, Ion Exchange; Dogs; Fluorenes; Microsomes, Liver; Nitrophenols; Octoxynol; Polyethylene Glycols