In vivo and in vitro toxicokinetics including metabolism, isozyme mapping, and monoamine oxidase inhibition of three (2-aminopropyl)benzo[b]thiophene (APBT) psychedelics.

Three recently identified psychedelics and entactogens—3-APBT, 5-APBT, and 6-APBT—activate serotonin 2 receptor subtypes and cause head-twitch responses in mice. Their toxicokinetics, metabolism, and monoamine oxidase (MAO) inhibition were characterized using liquid chromatography-high-resolution tandem mass spectrometry. Metabolites were identified in urine from male Wistar rats over 24 hours after oral administration (2 mg/kg) and in incubations with pooled human liver S9 fraction (25 µM). Hydroxylation, primarily catalyzed by CYP1A2, CYP2D6, CYP3A4, and CYP3A5, was the main phase I biotransformation; phase II reactions included N-acetylation, glucuronidation, and sulfation. All three isomers strongly inhibited MAO-A (IC50: 5-APBT 0.4 µM, 6-APBT 0.6 µM, 3-APBT 4 µM) but only weakly inhibited MAO-B (IC50 23-49 µM). Clinically relevant MAO-A inhibition and associated interaction risks cannot be excluded.

Study at a glance

Abstract

3-(2-Aminopropyl)benzo[b]thiophene (3-APBT), 5-APBT, and 6-APBT are recently identified psychedelics and entactogens that activate serotonin 2 receptor subtypes and lead to a head-twitch response in mice. The present study characterized their toxicokinetics, metabolism, and monoamine oxidase (MAO) inhibition using liquid chromatography-high-resolution tandem mass spectrometry. Metabolites were tentatively identified in urine from male Wistar rats collected over 24 h after oral administration (2 mg/kg body weight) and in incubations with pooled human liver S9 fraction (25 µM after 1 and 6 h). Phase I isoenzyme mapping and MAO inhibition were assessed using individual incubations with 11 human monooxygenases or recombinant human MAO-A and MAO-B. Hydroxylation was the predominant phase I biotransformation, primarily catalyzed by cytochrome P450 (CYP) 1A2, CYP2D6, CYP3A4, and CYP3A5, while N-acetylation, glucuronidation, and sulfation were observed as phase II reactions. The metabolic patterns were similar to those of related 5- and 6-(2-aminopropyl)benzofuran analogues, and the involvement of multiple CYP isozymes suggested a reduced toxicity risk e.g., by CYP-mediated drug-drug interactions. However, all three APBT isomers strongly inhibited MAO-A (IC50 of 5-APBT 0.4 µM, 6-APBT 0.6 µM, and 3-APBT 4 µM) but only weakly MAO-B (IC50 23-49 µM). Given that the MAO-A inhibition strengths of 5-APBT and 6-APBT were in the range of model inhibitors, clinically relevant MAO-A inhibition and associated interaction risks and toxic effects cannot be excluded. These data provide a toxicokinetic basis to support the clinical and forensic interpretation of exposures to APBT and related sulfur-based psychedelics.