1-Aminobenzotriazole, a Known Cytochrome P450 Inhibitor, Is a Substrate and Inhibitor of N-Acetyltransferase

Abstract

ABSTRACT:1-Aminobenzotriazole (ABT) has been used widely as a nonselective in vitro and in vivo inhibitor of cytochrome P450 enzymes. To date, however, it has not been evaluated as an inhibitor of UDPglucuronosyltransferase (UGT), sulfotransferase (SULT), and Nacetyltransferase (NAT). In the present study, ABT was shown not to inhibit UGT and SULT activity (acetaminophen and 7-hydroxycoumarin as substrates) in rat liver microsomes and rat liver 9000g supernatant fraction (RLS9), respectively. However, it did inhibit the RLS9-catalyzed N-acetylation of procainamide (IC 50 ϳ 30 M), and no preincubation time dependence was evident. In agreement, oral ABT (100 mg/kg, 2 h predose) decreased the clearance of intravenous procainamide (45%) in rats, accompanied by a decreased N-acetylprocainamide-to-procainamide ratio in urine (0.74 versus 0.21) and plasma (area under the curve ratio 0.59 versus 0.11). Additional studies with human forms of NAT (hNAT1 and hNAT2) revealed that ABT is a more potent inhibitor of hNAT2 compared with hNAT1 (IC 50 158 M versus > 1 mM). Consistent with the IC 50 estimate, formal inhibition studies revealed that inhibition of hNAT2 was competitive with an inhibition constant of 67 M. In accordance with the competitive inhibition, ABT was shown to undergo N-acetylation in the presence of both human NAT forms, with hNAT1 exhibiting less activity under the same assay conditions (ϳ40% of hNAT2). In summary, the results described herein indicate that ABT is a substrate and inhibitor of NAT. Such an interaction should be considered when using ABT as a nonselective inhibitor of P450, especially when NAT-dependent metabolism is also involved.

Rate-Determining and Rate-Limiting Steps in the Clearance and Excretion of a Potent and Selective p21-Activated Kinase Inhibitor: A Case Study of Rapid Hepatic Uptake and Slow Elimination in Rat

“…In vitro , ABT at 500 μM completely inhibited both oxidative and N- acetylation metabolism in mouse hepatocytes (supplemental data). This is consistent with the literature showing that the pan-P450 inhibitor, ABT, is also a potent inhibitor of N -acetyltrans-
ferase [31]. Based on this paper by Sun et al , when ABT was dosed orally in vivo at 100 mg/kg (2 h predose) with procainamide (IV), the clearance of procainamide was reduced by 45%.…”

Inhibition of Cytochromes P450 and the Hydroxylation of 4-Monochlorobiphenyl in Whole Poplar

“…ABT is a well-known nonselective substrate inhibitor of both human and nonhuman CYPs in vitro and in vivo . It has been used extensively to distinguish CYP-mediated metabolism from non-CYP-mediated metabolism in vitro (21-24). Furthermore, ABT has also been proven to be safe in rats after an acute high dose and upon multiple dosing, making it an attractive agent for differentiating parent- or metabolite-based toxicities in safety assessment studies (25-26).…”

Permeability Comparison between Hepatocyte and Low Efflux MDCKII Cell Monolayer

“…However, the method is quite laborious and requires a large amount of experimental data at varying time points. This approach uses 1-aminobenzotriazole (ABT) to inhibit CYP enzyme metabolism, which could also lead to inaccuracy in estimating permeability, due to incomplete inhibition of CYPs (15) and low selectivity towards other enzymes (16). In addition, when the mechanistic model is used without prior data transformation to delineate passive from active uptake into the cell, great uncertainty may be associated with the determination of passive permeability and intracellular unbound fraction (10).…”