Elucidating the Phase I metabolism of psilocin in vitro

Psilocin is a well-studied controlled substance with potential psychotherapeutic applications. However, research gaps remain regarding its metabolism. Our objective was to elucidate a comprehensive Phase I metabolic profile of psilocin to support its forensic management and clinical development. We utilized human enzymes from various sources to characterize the Phase I metabolism of psilocin and estimated its hepatic and extrahepatic clearances via in vitro to in vivo extrapolation. We identified 2-(4-hydroxy-1H-indol-3-yl)-acetaldehyde (4-HIA) as the Phase I intermediate metabolite for the first time. Psilocin was metabolized to 4-HIA by monoamine oxidase A (MAO-A), and further metabolized to the terminal metabolite 2-(4-hydroxy-1H-indol-3-yl)-acetic acid (4-HIAA) by cytosolic aldehyde oxidase (AO) and aldehyde dehydrogenases (ALDHs). MAO-A-mediated hepatic clearance of psilocin (CL_H,MAO-A) was estimated to be 158.74 mL/min, accounting for 80.9% of the total hepatic metabolism of psilocin (CL_H,all). MAO-A primarily contributed to the Phase I metabolism of psilocin. Total MAO-A-mediated organ clearance (CL_{all organs,MAO-A}) was estimated to be 614.81 mL/min, with CL_H,MAO-A accounting for 25.8%, indicating extensive MAO-A-mediated extrahepatic clearance of psilocin. Overall, our study sheds novel insights on Phase I metabolic pathway of psilocin and illuminated the importance of MAO-A-mediated hepatic and extrahepatic clearances of psilocin.