AhR activation underlies the CYP1A autoinduction by A-998679 in rats

Characterization of JNJ-2482272 [4-(4-Methyl-2-(4-(Trifluoromethyl)Phenyl)Thiazole-5-yl) Pyrimidine-2-Amine] As a Strong Aryl Hydrocarbon Receptor Activator in Rat and Human

[4-(4-Methyl-2-(4-(trifluoromethyl)phenyl)thiazole-5-yl)pyrimidine-2-amine] (JNJ-2482272), under investigation as an anti-inflammatory agent, was orally administered to rats once daily at 60 mg/kg for 6 consecutive days. Despite high plasma exposure after single administration (C_max of 7.1 μM), JNJ-2482272 had plasma concentrations beneath the lower limit of quantification (3 ng/ml) after 6 consecutive days of dosing. To determine if JNJ-2482272 is an autoinducer in rats, plated rat hepatocytes were treated with JNJ-2482272 for 2 days. The major hydroxylated metabolites of JNJ-2482272 were isolated and characterized by mass spectrometry and NMR analyses. Compared with the vehicle-treated cells, a concentration-dependent increase was observed in the formation of phase I- and II-mediated metabolites coinciding with greater expression of cytochrome P450s (P450s) and UDP-glucuronosyltransferases (UGTs) in rat hepatocytes. CYP1A1, CYP1A2, CYP1B1, and UGT1A6 transcripts were predominantly induced, suggesting that JNJ-2482272 is an activator of the aryl hydrocarbon receptor (AhR). In a human AhR reporter assay, JNJ-2482272 demonstrated potent AhR activation with an EC₅₀ value of 0.768 nM, a potency more comparable to the strong AhR activator and toxin 2,3,7,8-tetrachloro-dibenzodioxin than to weaker AhR activators 3-methylcholanthrene, β-naphthoflavone, and omeprazole. In plated human hepatocytes, JNJ-2482272 induced CYP1A1 gene expression with an EC₅₀ of 20.4 nM and increased CYP1A activity >50-fold from basal levels. In human recombinant P450s, JNJ-2482272 was exclusively metabolized by the CYP1 family of enzymes and most rapidly by CYP1A1. The summation of these in vitro findings bridges the in vivo conclusion that JNJ-2482272 is a strong autoinducer in rats and potentially in humans through potent AhR activation. SIGNIFICANCE STATEMENT: Drugs that induce their own metabolism (autoinducers) can lack sustained exposures for pharmacology and safety assessment hindering their development. JNJ-2482272 is demonstrated herein as a strong aryl hydrocarbon receptor (AhR) activator and CYP1A autoinducer, explaining its near complete loss of exposure after repeat administration in rat, which is likely translatable to human (if progressed further) considering its nanomolar potency comparable to "classical" AhR ligands like 2,3,7,8-tetrachloro-dibenzo-dioxin despite bearing a "nonclassical" drug structure.

High-Fat Diets Alter the Modulatory Effects of Xenobiotics on Cytochrome P450 Activities

Cytochrome P450 monooxygenase (P450) enzymes metabolize critical endogenous chemicals and oxidize nearly all xenobiotics. Dysregulated P450 activities lead to altered capacity for drug metabolism and cellular stress. The effects of mixed exposures on P450 expression and activity are variable and elusive. A high-fat diet (HFD) is a common exposure that results in obesity and associated pathologies including hepatotoxicity. Herein, we report the effects of cigarette smoke on P450 activities of normal weight and HFD induced obese mice. Activity-based protein profiling results indicate that HFD mice had significantly decreased P450 activity, likely instigated by proinflammatory chemicals, and that P450 enzymes involved in detoxification, xenobiotic metabolism, and bile acid synthesis were effected by HFD and smoke interaction. Smoking increased activity of all lung P450 and coexposure to diet effected P450 2s1. We need to expand our understanding of common exposures coupled to altered P450 metabolism to enhance the safety and efficacy of therapeutic drug dosing.

Changes in coumarin kinetics and subcellular localization of CYP2E1 contribute to bile duct damage and reduce hepatocellular damage after repeated administration of coumarin in rats

Coumarin exhibits different hepatotoxicity in rats depending on the administration frequency. To investigate the underlying mechanisms for the differences, we administered coumarin to rats as a single dose or repeatedly for 4 weeks. We found large increases in blood levels of liver enzymes and noticeable centrilobular hepatic necrosis after a single dose of coumarin. After repeated administration, enzyme levels mildly increased, while those of γ-GTP and total bilirubin significantly increased, suggesting bile duct damage. In the control group, cytochrome P450 2E1 (CYP2E1) showed a diffuse subcellular distribution but accumulated within the hepatocyte endoplasmic reticulum after repeated coumarin administration. The maximum blood concentrations of coumarin and its metabolites were significantly lower upon repeated administration. The results suggest that changes in coumarin pharmacokinetics and CYP2E1 subcellular distribution contribute to resistance to coumarin-induced hepatic necrosis, while cytotoxicity of metabolic conjugates shown in vitro may contribute to bile duct damage upon repeated coumarin administration.

Impact of aminophylline on the pharmacodynamics of propofol in beagle dogs

This study aimed to characterize pharmacodynamic interaction between propofol and aminophylline. Nine beagle dogs were randomly allocated at the propofol rates of 0.75 (group A), 1.00 (group B), and 1.25 (group C) mg/kg/min. During period 1, propofol only was infused, while during period 2, aminophylline only, at the rate of 0.69 (group A), 1.37 (group B), and 2.62 (group C) mg/kg/h. During periods 3-5, the two drugs were co-administered. The aminophylline infusion rate was 0.69 (period 3), 1.37 (period 4), and 2.62 (period 5) mg/kg/h. The aminophylline was infused from 0 to 30 h, and the propofol was infused at 24 h for 20 min. Blood samples and electroencephalograms were obtained at preset intervals. In the linear regression between log-transformed doses of aminophylline and AUC inf, the slope was 0.6976 (95% CI 0.5242-0.8710). Pharmacokinetics of aminophylline was best described by a one-compartment, with enzyme auto-induction, model. Pharmacokinetics and pharmacodynamics of propofol were best described by a three-compartment model and a sigmoid Emax model, respectively. Pharmacodynamic parameter estimates of propofol were: k(e0) = 0.805/min, E0 = 0.76, Emax = 0.398, Ce(50 na) = 2.38 μg/mL (without aminophylline-exposure), C(e50 wa) = 4.49 μg/mL (with aminophylline-exposure), and γ = 2.21. Propofol becomes less potent when exposed to aminophylline. Pharmacodynamic antagonistic interaction of aminophylline with propofol sedation, may occur, not in a dose-dependent manner, but in an all-or-none response.

Enrichment with wood blocks does not affect toxicity assessment in an exploratory toxicology model using Sprague-Dawley rats

Environmental enrichment in rodents may improve animal well-being but can affect neurologic development, immune system function, and aging. We tested the hypothesis that wood block enrichment affects the interpretation of traditional and transcriptomic endpoints in an exploratory toxicology testing model using a well-characterized reference compound, cyclophosphamide. ANOVA was performed to distinguish effects of wood block enrichment separate from effects of 40 mg/kg cyclophosphamide treatment. Biologically relevant and statistically significant effects of wood block enrichment occurred only for body weight gain. ANOVA demonstrated the expected effects of cyclophosphamide on food consumption, spleen weight, and hematology. According to transcriptomic endpoints, cyclophosphamide induced fewer changes in gene expression in liver than in spleen. Splenic transcriptomic pathways affected by cyclophosphamide included: iron hemostasis; vascular tissue angiotensin system; hepatic stellate cell activation and fibrosis; complement activation; TGFβ-induced hypertrophy and fibrosis; monocytes, macrophages, and atherosclerosis; and platelet activation. Changes in these pathways due to cyclophosphamide treatment were consistent with bone marrow toxicity regardless of enrichment. In a second study, neither enrichment nor type of cage flooring altered body weight or food consumption over a 28-d period after the first week. In conclusion, wood block enrichment did not interfere with a typical exploratory toxicology study; the effects of ingested wood on drug level kinetics may require further consideration.

Transcriptomic evaluation of canine suspension-shipped and pre-plated hepatocytes: comparison to liver

INTRODUCTION

In vitro assays using rat and human hepatocytes are used for hepatotoxicity studies; however, in vitro methods are less established for canine hepatocytes. In particular, little is known about the effects of plating and culture on canine hepatocytes. The goal of this study was to conduct a descriptive analysis of an in vitro canine hepatocyte system to evaluate its utility and limitations. The study objectives were to determine if canine hepatocytes shipped in suspension or pre-plated were transcriptomically different from one another and their liver of origin, and to understand temporal transcriptomic changes.

MATERIALS AND METHODS

Frozen canine liver samples were delivered on dry ice; hepatocytes from these livers were delivered in a cell/media suspension (S) or pre-plated (P). Hepatocytes were harvested at arrival and after up to 120 hr of culture in naïve media, or after 48 hr treatment with prototypical enzyme inducing xenobiotics (phenobarbital or rifampin).

RESULTS

A global transcriptomic comparison between liver and hepatocyte preparations indicated that the transcriptome was affected post-plating; transporters and genes involved in xenobiotic metabolism were generally down-regulated. Basal mRNA levels of CYP3A12 and CYP2B11 decreased temporally; after 120 hr CYP3A12 levels decreased by 1000-fold. CYP3A12 and CYP2B11 induction after phenobarbital or rifampin treatment was robust in both cell types but stronger in S cells.

CONCLUSIONS

These results indicate that S and P hepatocytes cultured under the current conditions are appropriate for specific in vitro tests. Further characterization of endpoints should be conducted for a thorough understanding of the model's limitations.