Short-term toxicity study of 1-aminobenzotraizole, a CYP inhibitor, in Wistar rats

1-Aminobenzotriazole (ABT) is a pan-specific, mechanism-based inhibitor of CYP P450 enzymes, often used as co-treatment to investigate the metabolism-dependent toxicity of drugs or chemicals. To assess the confounding effects of ABT in such kind of mechanistic studies, a repeated dose toxicity study with ABT following 7 days oral administration at 0, 25, 50 and 100 mg/kg/day was performed in Wistar rats (5 rats/sex/group). Wistar rat is selected as a model being one of the well characterized rodent species, widely used for toxicity and toxicokinetics studies. The standard parameters of general toxicity study viz. clinical signs, body weight, feed consumption, clinical, gross and histopathology were evaluated. The ABT was tolerated up to the highest tested dose of 100 mg/kg/day. No clinical signs, mortality or effect on feed consumption at any dose. Slight increase in body weight gain was noted in ABT treated females. Increased reticulocyte, and decreased triglycerides, BUN, A/G ratio and plasma potassium; increased weight of liver, kidneys, adrenals and thyroid was noted in ABT treated animals. Microscopically, hypertrophic findings were noted in liver, thyroid, adrenal glands, pituitary and uterus. Some of these changes were observed at as low as 25 mg/kg/day, therefore, NOEL could not be established. Based on this study, it is concluded that ABT is tolerable up to 100 mg/kg/day with some variations in clinical pathology, organ weight and histopathology; these changes should be considered during the assessment of any mechanistic study with ABT. Findings of this manuscript were presented at 58th meeting of the Society of Toxicology, Baltimore, 11 March 2019.

1-Aminobenzotriazole: A Mechanism-Based Cytochrome P450 Inhibitor and Probe of Cytochrome P450 Biology

1-Aminobenzotriazole (1-ABT) is a pan-specific, mechanism-based inactivator of the xenobiotic metabolizing forms of cytochrome P450 in animals, plants, insects, and microorganisms. It has been widely used to investigate the biological roles of cytochrome P450 enzymes, their participation in the metabolism of both endobiotics and xenobiotics, and their contributions to the metabolism-dependent toxicity of drugs and chemicals. This review is a comprehensive evaluation of the chemistry, discovery, and use of 1-aminobenzotriazole in these contexts from its introduction in 1981 to the present.

Utility of food pellets containing 1-aminobenzotriazole for longer term in vivo inhibition of cytochrome P450 in mice

1. The utility of 1-aminobenzotriazole (ABT), incorporated in food, has been investigated as an approach for longer term inhibition of cytochrome P450 (P450) enzymes in mice. 2. In rats, ABT inhibits gastric emptying, to investigate this potential limitation in mice we examined the effect of ABT administration on the oral absorption of NVS-CRF38. Two hour prior oral treatment with 100 mg/kg ABT inhibited the oral absorption of NVS-CRF38, T_max was 4 hours for ABT-treated mice compared to 0.5 hours in the control group. 3. A marked inhibition of hepatic P450 activity was observed in mice fed with ABT containing food pellets for 1 month. P450 activity, as measured by the oral clearance of antipyrine, was inhibited on day 3 (88% of control), week 2 (83% of control) and week 4 (80% of control). 4. T_max values for antipyrine were comparable between ABT-treated mice and the control group, alleviating concerns about impaired gastric function. 5. Inclusion of ABT in food provides a minimally invasive and convenient approach to achieve longer term inhibition of P450 activity in mice. This model has the potential to enable pharmacological proof-of-concept studies for research compounds which are extensively metabolised by P450 enzymes.

Exposure of Heligmosomoides polygyrus and Trichuris muris to albendazole, albendazole sulfoxide, mebendazole and oxantel pamoate in vitro and in vivo to elucidate the pathway of drug entry into these gastrointestinal nematodes

Millions of people are treated with anthelmintics to control soil-transmitted helminth infections; yet, drug distribution in the plasma and gastrointestinal tract compartments and the pathway of drug uptake into gastrointestinal nematodes responsible for the pharmacological effect are unknown. We assessed the distribution and uptake of albendazole, albendazole sulfoxide, albendazole sulfone in the hookworm Heligmosomoides polygyrus in vitro and in vivo as well as the distribution and uptake of albendazole, mebendazole, and oxantel pamoate in the whipworm Trichuris muris in vitro and in vivo. Oral and intraperitoneal treatments (100 mg/kg) were studied. Drug quantities in helminths and host compartments (stomach, the contents and mucosa of the small and large intestine, and the plasma) were determined using HPLC-UV/vis and anthelmintic activities were recorded using phenotypic readout. The influence of 1-aminobenzotriazole (ABT), an irreversible and unspecific cytochrome P450 inhibitor, on albendazole disposition in mice harboring H. polygyrus was evaluated. In vivo, albendazole was found in quantities up to 10 nmol per ten H. polygyrus and up to 31 nmol per ten T. muris. ABT did not change the levels of albendazole or its metabolites in the plasma of mice harboring H. polygyrus or in H. polygyrus, whereas drug levels in the gastrointestinal tract of host mice doubled. Mebendazole and oxantel pamoate quantities per ten T. muris were as high as 21 nmol and 34 nmol, respectively. Albendazole revealed a very dynamic distribution and high rate of metabolism, hence, H. polygyrus and T. muris are exposed to albendazole and both metabolites via multiple pathways. Diffusion through the cuticle seems to be the crucial pathway of oxantel pamoate uptake into T. muris, and likely also for mebendazole. No relationship between concentrations measured in helminths and concentrations in plasma, intestinal content and mucosa of mice, or drug efficacy was noted for any of the drugs studied.

In vivo use of the CYP inhibitor 1-aminobenzotriazole to increase long-term exposure in mice

1-Aminobenzotriazole (ABT) is a well-known in vivo nonspecific inhibitor of cytochrome P450 (CYP) enzymes. An effective dosing regimen of ABT for a multiple-administration study is needed to conduct pharmacological studies for proof-of-concept, although it has been established for single-administration study, to characterize the pharmacokinetics of drug candidates. This study demonstrated a suitable dosing vehicle of ABT for continuous administration and increased exposure to antipyrine, which is a nonspecific probe of CYP, using ABT for a long period in mice. The dosing vehicle of ABT was 0.5% (w/v) hydroxypropyl methylcellulose and 0.5% (v/v) Tween 80 in N,N-dimethylacetamide/20% hydroxypropyl-β-cyclodextrin aqueous solution (2:8, v/v) based on the duration of apparent solubility. After implantation of an ALZET osmotic pump with ABT, the plasma concentrations of ABT were maintained at more than 4.1 μg/ml over 336 h. Compared with the vehicle group, the CLtot of antipyrine with ABT decreased to approximately one-fourth, and the BA of antipyrine with ABT increased up to 3-fold. In addition, the enhancement of exposure of antipyrine by ABT was maintained over the 336 h. The body weight, food consumption and hematological parameters of mice did not change with ABT administration for 16 days. These findings demonstrated that pretreatment of ABT can increase long-term exposure using continuous administration with the ALZET osmotic pump in mice with no overt toxicity. It is concluded that the in vivo use of 1-aminobenzotriazole can be applied to pharmacological studies for proof-of-concept, thus contributing to the selection of drug candidates at an early drug discovery stage. Copyright © 2016 John Wiley & Sons, Ltd.

Application of Osmotic Pumps for Sustained Release of 1-Aminobenzotriazole and Inhibition of Cytochrome P450 Enzymes in Mice: Model Comparison with the Hepatic P450 Reductase Null Mouse

The effectiveness of controlled release 1-aminobenzotriazole (ABT) administration to inhibit cytochrome P450 (P450) enzymes has been evaluated in mice. To maximize the duration of P450 inhibition in vivo, ABT was administered via an osmotic pump. The degree of P450 inhibition was compared with that achieved with a single bolus dose of ABT. Two-hour prior subcutaneous treatment of mice with ABT (50 mg/kg) inhibited antipyrine clearance by 88%. A less pronounced inhibitory effect (29% reduction in clearance) was observed when ABT was administered 24-hours before antipyrine administration, indicating partial restoration of P450 activity during this longer pretreatment time. The duration of ABT in mice was very short (mean residence time = 1.7 hours) after subcutaneous bolus administration. When the inhibitor was delivered by an osmotic pump, maximum blood concentrations of the inhibitor were observed 24 hours after device implantation and were maintained at steady state for 6 days. Inhibition of P450 activity, as measured by antipyrine clearance, was confirmed at 24 hours and 120 hours after pump implantation, highlighting the utility of this method as a longer-term model for P450 inhibition in mice. The magnitude of P450 inhibition in ABT-treated mice was compared with that in hepatic P450 reductase null mice and both models were comparable. In vivo ABT administration by an osmotic pump offers an effective approach for longer-term P450 inhibition in mice and avoids the necessity for multiple dosing of the inhibitor.

Species Differences in the Oxidative Desulfurization of a Thiouracil-Based Irreversible Myeloperoxidase Inactivator by Flavin-Containing Monooxygenase Enzymes

N1-Substituted-6-arylthiouracils, represented by compound 1 [6-(2,4-dimethoxyphenyl)-1-(2-hydroxyethyl)-2-thioxo-2,3-dihydropyrimidin-4(1H)-one], are a novel class of selective irreversible inhibitors of human myeloperoxidase. The present account is a summary of our in vitro studies on the facile oxidative desulfurization in compound 1 to a cyclic ether metabolite M1 [5-(2,4-dimethoxyphenyl)-2,3-dihydro-7H-oxazolo[3,2-a]pyrimidin-7-one] in NADPH-supplemented rats (t1/2 [half-life = mean ± S.D.] = 8.6 ± 0.4 minutes) and dog liver microsomes (t1/2 = 11.2 ± 0.4 minutes), but not in human liver microsomes (t1/2 > 120 minutes). The in vitro metabolic instability also manifested in moderate-to-high plasma clearances of the parent compound in rats and dogs with significant concentrations of M1 detected in circulation. Mild heat deactivation of liver microsomes or coincubation with the flavin-containing monooxygenase (FMO) inhibitor imipramine significantly diminished M1 formation. In contrast, oxidative metabolism of compound 1 to M1 was not inhibited by the pan cytochrome P450 inactivator 1-aminobenzotriazole. Incubations with recombinant FMO isoforms (FMO1, FMO3, and FMO5) revealed that FMO1 principally catalyzed the conversion of compound 1 to M1. FMO1 is not expressed in adult human liver, which rationalizes the species difference in oxidative desulfurization. Oxidation by FMO1 followed Michaelis-Menten kinetics with Michaelis-Menten constant, maximum rate of oxidative desulfurization, and intrinsic clearance values of 209 μM, 20.4 nmol/min/mg protein, and 82.7 μl/min/mg protein, respectively. Addition of excess glutathione essentially eliminated the conversion of compound 1 to M1 in NADPH-supplemented rat and dog liver microsomes, which suggests that the initial FMO1-mediated S-oxygenation of compound 1 yields a sulfenic acid intermediate capable of redox cycling to the parent compound in a glutathione-dependent fashion or undergoing further oxidation to a more electrophilic sulfinic acid species that is trapped intramolecularly by the pendant alcohol motif in compound 1.