Renal excretion profiles of psilocin following oral administration of psilocybin: a controlled study in man

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Abstract

In a clinical study eight volunteers received psilocybin (PY) in psychoactive oral doses of 212±25 μg/kg body weight. To investigate the elimination kinetics of psilocin (PI), the first metabolite of PY, urine was collected for 24 h and PI concentrations were determined by high-performance liquid chromatography with column switching and electrochemical detection (HPLC-ECD). Sample workup included protection of the unstable PI with ascorbic acid, freeze-drying, and extraction with methanol. Peak PI concentrations up to 870 μg/l were measured in urine samples from the 2–4 h collection interval. The PI excretion rate in this period was 55.5±33.8 μg/h. The limit of quantitation (10 μg/L) was usually reached 24 h after drug administration. Within 24 h, 3.4±0.9% of the applied dose of PY was excreted as free PI. Addition of β-glucuronidase to urine samples and incubation for 5 h at 40 °C led to twofold higher PI concentrations, although 18±7% of the amount of unconjugated PI was decomposed during incubation. We conclude that in humans PI is partially excreted as PI-O-glucuronide and that enzymatic hydrolysis extends the time of detectability for PI in urine samples.

Introduction

Psilocybin (PY, Fig. 1) is a psychoactive indolealkylamine with a unique hallucinogenic profile. The widespread use of PY-containing mushrooms (e.g. Psilocybe cubensis, Psilocybe semilanceata) as a recreational drug is well documented [1], [2], [3], [4], [5]. The increasing popularity of ‘magic mushrooms’ is also due to the relatively easy access to psychoactive fungi and cultivation kits via the Internet [6] and ‘smart shops’ in Europe. In recent years, PY also has become an important experimental tool to study the neurobiological basis of altered states of consciousness. An increasing number of scientific publications reveal a renaissance of research with PY [7], [8], [9], [10], [11], [12], [13], [14], [15]. In contrast to these projects, mostly dealing with the “model-psychosis” paradigm, only a few studies have investigated the pharmacokinetic properties of PY in man [16], [17], [18], [19]. In vivo, PY is rapidly dephosphorylated to the pharmacologically active hydroxy metabolite psilocin (PI, Fig. 1) [17], [18], [19]. Investigations in rats [20] and humans [16], [17], [18] revealed the metabolic formation of 4-hydroxyindol-3-yl-acetic acid (4-HIAA) and 4-hydroxytryptophol (4-HTP) by deamination and oxidation of PI.

Eivindvik and Rasmussen [21] postulated the formation of psilocin-O-glucuronide (PI-G, Fig. 1) in a manner analogous to the formation of 5-hydroxytryptamine-O-glucuronide in serotonin metabolism. Recently, Sticht and Käferstein [22] analyzed PI in urine and serum from a recreational mushroom user. Their analysis of the untreated urine found 0.23 mg PI/l. When the urine was first treated with glucuronidase, however, they measured 1.76 mg PI/l, clearly implicating the formation of the glucuronide. The corresponding concentrations for PI in serum were 0.052 mg/l (total) and 0.018 mg/l (unconjugated), respectively. The isolation of PI-G from biological samples and confirmation of the chemical structure by spectroscopic methods has not yet been performed, thus direct evidence for the existence of this metabolite is still lacking. Nevertheless, the manifold higher concentrations of PI measured after sample hydrolysis and the selectivity of the β-glucuronidase used for conjugate cleavage in the experiments of Sticht and Käferstein [22] strongly support the hypothesis of metabolic formation of PI-G in humans.

Up to the present, only a very limited number of analytical methods for the determination of PI in biological samples have been published. Paper chromatography [20], [23] and later high-performance liquid chromatography with electrochemical detection (HPLC-ECD) [24] were used to investigate the metabolism of PY in rats. For metabolism studies in humans, HPLC-ECD methods with different sample workup strategies (liquid–liquid extraction and automated on-line solid-phase extraction) were established [16], [19]. For use in the field of forensic toxicology, a method involving gas chromatography–mass spectrometry (GC–MS) after derivatization of PI with N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) was recently published [22]. For reliable determination of PI and 4-HIAA in plasma samples obtained from two clinical trials investigating the pharmacokinetic properties of oral and intravenous PY in man, we established a novel HPLC–ECD method with column-switching [17], [18]. In contrast to other methods, sample workup includes protection of the highly oxidation-labile phenolic analytes [17], [18], [19] with ascorbic acid, freeze-drying, and in-vitro microdialysis. In order to achieve a more complete characterization of the PY pharmacokinetics derived from PI-plasma concentration data investigated in two earlier clinical studies [17], [18], the analytical method was also adapted for determination of PI in urine samples. Validation of the modified analytical method, renal excretion profiles of free and conjugated PI, as well as pharmacokinetic estimates derived from eight volunteers receiving active oral doses of PY are presented in this paper.

Section snippets

Study design

The clinical study in humans investigating the urinary excretion profiles of PI was approved by the Ethics Committee of the University Hospital of Psychiatry, Zürich (PUK-ZH). The administration of PY to healthy volunteers under controlled conditions was authorized by the Swiss Federal Office for Public Health, Department of Pharmaceutics and Narcotics, Bern. Volunteers were recruited by word-of-mouth within the University of Bern and the PUK-ZH. The subjects were four female and four male

Psychotropic effects of PY

Oral doses of 10–18 mg PY induced markedly altered states of consciousness (ASC) in all volunteers. During the peak effect of the drug 60–90 min after intake (lasting 1–2 h), the subjects experienced pronounced changes in sensory perception, affect and mood, thought processes, and ego functioning. Alterations in perception of time and space as well as visual illusions, complex hallucinations and synaesthesias were frequently observed. The PY dose employed in our study was well tolerated, with

Acknowledgements

The authors are grateful to Dr. Truls Baer and Sabina Sperisen for their support during the clinical study and wish to thank Dr. Thomas Lehmann and Dr. Hansjörg Helmlin for their help in solving several analytical problems and Dr. Theodor Huber for the physical examinations of the volunteers. We especially thank Dr. Alexander Shulgin and Dr. David Nichols for critical comments on the manuscript. This study was financially supported in part by the Swiss National Science Research Foundation

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