The potential contribution of embryonic N-acetyltransferase to 4-aminobiphenyl genotoxicity

Abstract

The studies presented in this dissertation were designed to test the hypothesis that embryonic N-acetyltransferase (NAT) acetylates 4-aminobiphenyl (4ABP), potentially affecting embryonic aromatic amine toxicity. NAT1 and NAT2 mRNAs were detected in C57BL6/J mice in gestational day (GD) 10 embryo/placental tissue, GD 15 embryo and GD 15 placenta tissue, and GD 18 extrahepatic embryonic tissue. Only NAT2 mRNA was detected in GD 18 hepatic tissue. NAT1 was not found in GD 18 or neonatal day (ND) 3 liver. NAT activity was present at all three gestational time points where NAT mRNA was detected. 4ABP NAT activity increased as gestation advanced. Activity at ND 4 was 1.5 fold higher than GD 10 tissue and 1.2 fold higher than GD 15. Neonatal hepatic tissue showed very little difference between ND 2 and ND 4. Preliminary kinetic constants were determined for GD 18 through ND 4. The average Km was 74 muM and the average Vmax was 0.78 nmol/min/mg. Finally, in vivo studies were conducted to determine if there was embryonic exposure to 4ABP or 4AABP. The amount of 4ABP in embryonic or placental tissue remained constant over the three time periods tested. While the level of 4AABP in the placenta did not change during gestation, the amount of 4AABP detected in the GD 18 embryonic tissue increased significantly over the other time points. 5-15% of 4ABP and 20-30% of 4AABP maternal blood levels were detected in the embryonic/placental tissue. Less than 0.03% to 0.06% of the maternal dose was found to have been converted to 4AABP in embryonic tissue. In summary, (1) NAT1 and NAT2 mRNAs were found in embryonic tissue; (2) functional NAT protein was present in the embryo; and (3) 4ABP and 4AABP were found in the embryo following maternal exposure to 4ABP. This suggests that embryonic NAT may contribute to the developmental toxicity of aromatic amines.