Stereoselective urinary MDMA (ecstasy) and metabolites excretion kinetics following controlled MDMA administration to humans

Abstract

The R- and S-enantiomers of racemic 3,4-methylenedioxymethamphetamine (MDMA) exhibit different dose–concentration curves. In plasma, S-MDMA was eliminated at a higher rate, most likely due to stereoselective metabolism. Similar data were shown in various in vitro experiments. The aim of the present study was the in vivo investigation of stereoselective elimination of MDMA's phase I and phase II metabolites in human urine following controlled oral MDMA administration. Urine samples from 10 participants receiving 1.0 and 1.6 mg/kg MDMA separated by at least one week were analyzed blind by liquid chromatography–high resolution-mass spectrometry and gas chromatography–mass spectrometry after chiral derivatization with S-heptafluorobutyrylprolyl chloride. R/S ratios at C_max were comparable after low and high doses with ratios >1 for MDMA, free DHMA, and HMMA sulfate, and with ratios <1 for MDA, free HMMA, DHMA sulfate and HMMA glucuronide. In the five days after the high MDMA dose, a median of 21% of all evaluated compounds were excreted as R-stereoisomers and 17% as S-stereoisomers. Significantly greater MDMA, DHMA, and HMMA sulfate R-enantiomers and HMMA and HMMA glucuronide S-stereoisomers were excreted. No significant differences were observed for MDA and DHMA sulfate stereoisomers. Changes in R/S ratios could be observed over time for all analytes, with steady increases in the first 48 h. R/S ratios could help to roughly estimate time of MDMA ingestion and therefore, improve interpretation of MDMA and metabolite urinary concentrations in clinical and forensic toxicology.

Introduction

3,4-Methylenedioxymethamphetamine (MDMA) or Ecstasy, is a recreational drug of abuse popular among young people. Recently, the Substance Abuse and Mental Health Services Administration reported increasing MDMA consumption in the United States [1]. MDMA is usually consumed as a 1:1 racemate of R- and S-enantiomers. The S-enantiomer is more potent than the R-enantiomer in producing euphoria, energy and a desire to socialize [2], [3]. MDMA also can induce severe acute toxic symptoms, such as tachycardia, hypertension, hyperthermia, and hepatotoxicity [3], severe and fatal intoxications also have been described [3]. Concerning chronic toxicity, animal data suggest that MDMA causes irreversible damage to serotonergic nerve terminals in the central nervous system [3], [4], [5], [6]. In humans, chronic MDMA toxicity is still controversial, as some recent publications suggest that animal doses may be too high compared to human pharmacokinetics [7], [8], while others indicate that humans are susceptible to brain serotonin neurotoxicity [9]. Admittedly, direct MDMA injection into rat brain failed to reproduce neurotoxic effects seen after systemic administration [10]. Furthermore, alteration of cytochrome P450 (CYP)-mediated MDMA metabolism influenced MDMA-induced neurotoxicity [10], [11]. Therefore, MDMA metabolism may be an important contributor to neurotoxicity [12], [13], [14], [15].

In vivo and in vitro MDMA studies revealed two main metabolic pathways. One includes multiple CYP enzyme-catalyzed O-demethylenation of MDMA to 3,4-dihydroxymethamphetamine (DHMA), followed by catechol-O-methyltransferase (COMT)-catalyzed O-methylation, primarily to 4-hydroxy-3-methoxymethamphetamine (HMMA). DHMA and HMMA also may be conjugated by uridine diphosphate glucuronyltransferases (UGT) to DHMA 3-glucuronide, DHMA 4-glucuronide, and HMMA glucuronide, or by sulfotransferases (SULT) to DHMA 3-sulfate, DHMA 4-sulfate, and HMMA sulfate. A minor pathway includes demethylation to 3,4-methylendioxy-amphetamine (MDA) followed by demethylenation to 3,4-dihydroxy-amphetamine (DHA), O-methylation to 4-hydroxy-3-methoxyamphetamine (HMA), and conjugation [5], [16], [17], [18], [19], [20], [21].

During the first 48 h after racemic MDMA ingestion, the S-enantiomer was eliminated from plasma at a faster rate than the R-enantiomer [2], [3], [22], [23], [24], [25]. Enantioselective metabolism is the most likely explanation for different MDMA enantiomer pharmacokinetics in humans. In vitro experiments mediated by CYP, COMT, SULT and UGT enzymes documented preferential metabolism of S-enantiomers [19], [26], [27], [28].

Enantioselective metabolism and elimination data in human blood or urine following controlled MDMA administration are available [2], [24], [25]; however, in all of these, DHMA, HMMA, and/or HMA data were obtained after conjugate cleavage either by acidic or enzymatic hydrolysis (Helix pomatia). There are no data available following direct measurement of intact glucuronides and sulfates that also might show different enantiomeric ratios. The aim of the present study was to investigate in vivo excretion of chiral MDMA phase I and phase II metabolites in human urine following controlled oral MDMA administration.