In Vitro Metabolism of 25B-NBF, 2-(4-Bromo-2,5-Dimethoxyphenyl)-N-(2-Fluorobenzyl)ethanamine, in Human Hepatocytes Using Liquid Chromatography–Mass Spectrometry

25B-NBF, 2-(4-bromo-2,5-dimethoxyphenyl)-N-(2-fluorobenzyl)ethanamine, is a new psychoactive substance classified as a phenethylamine. It is a potent agonist of the 5-hydroxytryptamine receptor, but little is known about its metabolism and elimination properties since it was discovered. To aid 25B-NBF abuse screening, the metabolic characteristics of 25B-NBF were investigated in human hepatocytes and human cDNA-expressed cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes using liquid chromatography–high resolution mass spectrometry. At a hepatic extraction ratio of 0.80, 25B-NBF was extensively metabolized into 33 metabolites via hydroxylation, O-demethylation, bis-O-demethylation, N-debenzylation, glucuronidation, sulfation, and acetylation after incubation with pooled human hepatocytes. The metabolism of 25B-NBF was catalyzed by CYP1A1, CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2J2, CYP3A4, and UGT2B7 enzymes. Based on these results, it is necessary to develop a bioanalytical method for the determination of not only 25B-NBF but also its metabolites in biological samples for the screening of 25B-NBF abuse.

Molecular Structure-Based Prediction of the Toxicokinetics of Inhaled Vapors in Humans

The objectives of the present study were: (1) to evaluate the adequacy of setting hepatic extraction ratio (E) equal to 0 or 1 in physiologically based toxicokinetic (PBTK) models to generate the theoretically plausible envelope of venous blood concentration (Cv) profiles, and (2) to couple this approach with molecular structure-based estimation of blood:air and tissue: blood partition coefficients (PCs) to predictthe Cv profiles of volatile organic chemicals (VOCs) in humans. Setting E= 0 or 1 in PBTK models provided simulations of Cv envelopes that contained the Cv values determined in humans exposed to low concentrations of dichloromethane(DCM), ethylbenzene (EBZ), toluene (TOL), m-xylene(XYL), trichloroethy-lene (TCE), and 1,1,1-trichloroethane(TRI). Following the validation of using E= 0 or 1 in conventional PBTK models to predict the theoretically plausible envelope of Cv, a quantitative structure-toxicokinetic relationship (QSTkR) model was constructed. The QSTkR model used molecular structure information as the sole input to predict the PCs and considered E= 0 or 1 to generate simulations of the envelope of Cv. The experimental data on Cv were in most cases within the envelopes simulated using QSTkR models for DCM, EBZ, TOL, and XYL, but were outside the envelopes for TCE and TRI. The discrepancy observed between the Cv envelopes obtained using PBTK and QSTkR models can be explained by the fact that blood:air PCs of some VOCs were under-predicted while using molecular structure information. The modeling framework presented in this article represents the first animal-replacement tool that can provide a priori predictions of the toxicokinetic profiles of VOCs prior to laboratory experiments.

Estimation of the Hepatic Extraction Ratio of Indocyanine Green in Swine

1. The hepatic extraction ratio of Indocyanine Green was measured directly by trans-hepatic catheterization in 14 outbred swine (eight well-fed, six malnourished). A specific two-compartment pharmacokinetic model was fitted to the arterial Indocyanine Green concentration-time data and used to estimate the hepatic extraction ratio of Indocyanine Green. 2. The specific two-compartment pharmacokinetic model was modified to represent more accurately the physiological process of Indocyanine Green removal. Simulations were performed using this new model to estimate the hepatic extraction ratio of Indocyanine Green in the swine. 3. Similarly to previous findings, our data showed that the original model consistently overestimated the hepatic extraction ratio of Indocyanine Green (i.e. the model estimate was compared with the true, directly measured value). 4. The comparison of the modified model and the original model clearly indicates the reason for the overprediction of the hepatic extraction ratio of Indocyanine Green by the latter. The simulations using the new model indicate that the percentage of binding of Indocyanine Green to its transport protein (glutathione S-transferase) for removal in the bile will affect the estimation of the hepatic extraction ratio of Indocyanine Green. Thus, the amount of Indocyanine Green available for removal is less than that assumed by the original model.