Andrea E. Schwaninger

The Role of Human UDP-Glucuronyltransferases on the Formation of the Methylenedioxymethamphetamine (Ecstasy) Phase II Metabolites R- and S-3-Methoxymethamphetamine 4-O-Glucuronides

Different pharmacokinetic properties have been observed for the two enantiomers of the entactogen 3,4-methylendioxy-methamphetamine, most probably a result of enantioselective metabolism. The aim of the present work was to study the involvement of human UDP-glucuronyltransferase (UGT) isoforms in the glucuronidation of the enantiomers of its major metabolite 4-hydroxy-3-methoxymethamphetamine (HMMA). First, the reference standards of R- and S-HMMA-O-glucuronide were synthesized semipreparatively using the enzymes of rat liver microsomes, followed by isolation with semipreparative high-performance liquid chromatography and identification using mass spectrometry and NMR. Racemic HMMA was then incubated using heterologously expressed human UGTs and pooled human liver microsomes (HLMs), and the glucuronides were quantified by liquid chromatography-linear ion trap-mass spectrometry. UGT1A1, UGT1A3, UGT1A8, UGT1A9, UGT2B4, UGT2B7, UGT2B15, and UGT2B17 were involved in the glucuronidation of HMMA. UGT2B15, UGT2B17, and HLM revealed classic Michaelis-Menten kinetics, whereas UGT1A9 and UGT2B7 showed sigmoidal curves and the respective Eadie-Hofstee plots indicated autoactivation kinetics. UGT2B15 showed the highest affinity and activity. UGT2B15, UGT2B17, and HLMs were not considerably enantioselective but showed slight preferences for S-HMMA. Marked enantioselectivity could only be observed for UGT1A9 with respect to the S-enantiomer and for UGT2B7 with respect to the R-enantiomer. In conclusion, the O-glucuronidation of HMMA in vivo should not be expected to be enantioselective, and the different pharmacokinetic properties may not be caused directly by glucuronidation.

Development and validation of LC-HRMS and GC-NICI-MS methods for stereoselective determination of MDMA and its phase I and II metabolites in human urine.

3,4-Methylenedioxymethamphetamine (MDMA) is a racemic drug of abuse and its R- and S-enantiomers are known to differ in their dose-response curve. The S-enantiomer was shown to be eliminated at a higher rate than the R-enantiomer most likely explained by stereoselective metabolism that was observed in various in vitro experiments. The aim of this work was the development and validation of methods for evaluating the stereoselective elimination of phase I and particularly phase II metabolites of MDMA in human urine. Urine samples were divided into three different methods. Method A allowed stereoselective determination of the 4-hydroxy-3-methoxymethamphetamine (HMMA) glucuronides and only achiral determination of the intact sulfate conjugates of HMMA and 3,4-dihydroxymethamphetamine (DHMA) after C18 solid-phase extraction by liquid chromatography-high-resolution mass spectrometry with electrospray ionization. Method B allowed the determination of the enantiomer ratios of DHMA and HMMA sulfate conjugates after selective enzymatic cleavage and chiral analysis of the corresponding deconjugated metabolites after chiral derivatization with S-heptafluorobutyrylprolyl chloride using gas chromatography-mass spectrometry with negative-ion chemical ionization. Method C allowed the chiral determination of MDMA and its unconjugated metabolites using method B without sulfate cleavage. The validation process including specificity, recovery, matrix effects, process efficiency, accuracy and precision, stabilities and limits of quantification and detection showed that all methods were selective, sensitive, accurate and precise for all tested analytes.

Sulfation of the 3,4-methylenedioxymethamphetamine (MDMA) metabolites 3,4-dihydroxymethamphetamine (DHMA) and 4-hydroxy-3-methoxymethamphetamine (HMMA) and their capability to inhibit human sulfotransferases

3,4-Methylenedioxymethamphetamine (MDMA, Ecstasy) is excreted in human urine mainly as conjugates of its metabolites 3,4-dihydroxymethamphetamine (DHMA) and 4-hydroxy-3-methoxymethamphetamine (HMMA). The glucuronidation kinetics of HMMA showed high capacities, but also high K(m) values, unlikely to be reached after recreational users doses. Therefore, the aim of the present work was to investigate the sulfation of DHMA and HMMA by human sulfotransferases (SULTs) in pooled human liver cytosol (pHLC). The kinetic data showed deviation from typical Michaelis-Menten kinetics. The overall efficiency for HMMA sulfation was calculated to be 2-10 times higher than for glucuronidation. As the sulfation of both MDMA metabolites showed substrate inhibition effects, their inhibitory potential towards typical sulfation reactions in pHLC was tested. The following substrates for typical sulfation reactions were used: nitrophenol, dopamine, estradiol, and dehydroepi androsten dione. Inhibition was observed towards dopamine sulfation by DHMA and HMMA, but not by MDMA. The 1/V vs. 1/S plots indicated a mixed-type or competitive inhibition model for DHMA and HMMA, respectively. In conclusion, the presented data indicated that sulfation of HMMA should be the major conjugation reaction observed in humans. Furthermore, both, DHMA and HMMA, were identified as inhibitors of dopamine sulfation.

Urinary Excretion Kinetics of 3,4-Methylenedioxymethamphetamine (MDMA, Ecstasy) and Its Phase I and Phase II Metabolites in Humans following Controlled MDMA Administration

BACKGROUND 3,4-Methylendioxymethamphetamine (MDMA) is excreted inhuman urine as unchanged drug and phase I and II metabolites. Previous urinary excretion studies after controlled oral MDMA administration have been performed only after conjugate cleavage. Therefore, we investigated intact MDMA glucuronide and sulfate metabolite excretion. METHODS We used LC-high-resolution MS and GC-MS to reanalyze blind urine samples from 10 participants receiving 1.0 or 1.6 mg/kg MDMA orally. We determined median C(max),t(max), first and last detection times, and total urinary recovery; calculated ratios of sulfates and glucuronides; and performed in vitro-in vivo correlations. RESULTS Phase II metabolites of 3,4-dihydroxymethamphetamine (DHMA),4-hydroxy-3-methoxymethamphetamine (HMMA),3,4-dihydroxyamphetamine (DHA), and 4-hydroxy-3-methoxyamphetamine were identified, although only DHMA sulfates, HMMA sulfate, and HMMA glucuronide had substantial abundance. Good correlation was observed for HMMA measured after acid hydrolysis and the sum of unconjugated HMMA, HMMA glucuronide, and HMMA sulfate (R(2) = 0.87). More than 90% of total DHMA and HMMA were excreted as conjugates. The analyte with the longest detection time was HMMA sulfate. Median HMMA sulfate/glucuronide and DHMA 3-sulfate/4-sulfate ratios for the first 24 h were 2.0 and 5.3, respectively, in accordance with previous in vitro calculations from human liver microsomes and cytosol experiments. CONCLUSIONS Human MDMA urinary metabolites are primarily sulfates and glucuronides,with sulfates present in higher concentrations than glucuronides. This new knowledge may lead to improvements in urine MDMA and metabolite analysis in clinical and forensic toxicology, particularly for the performance of direct urine analysis.

Stereoselective Urinary MDMA (Ecstasy) and Metabolites Excretion Kinetics following Controlled MDMA Administration to Humans

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 MDMAs 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.

Investigation on the Enantioselectivity of the Sulfation of the Methylenedioxymethamphetamine Metabolites 3,4-Dihydroxymethamphetamine and 4-Hydroxy-3-Methoxymethamphetamine using the Substrate-Depletion Approach

Different pharmacokinetic properties are known for the two enantiomers of the entactogen 3,4-methylendioxy-methamphetamine (MDMA), most likely due to enantioselective metabolism. The aim of the present work was 1) the investigation of the main sulfotransferases (SULT) isoenzymes involved in the sulfation of the main MDMA phase I metabolites 3,4-dihydroxymethamphetamine (DHMA) and 4-hydroxy-3-methoxymethamphetamine (HMMA) and 2) the evaluation of a possible enantioselectivity of this phase II metabolic step. Therefore, racemic DHMA and HMMA were incubated with heterologously expressed SULTs, and quantification of the sulfates by liquid chromatography-high-resolution mass spectrometry was conducted. Because separation of DHMA and HMMA sulfate could not be achieved by liquid chromatography, enantioselective kinetic parameters were determined using the substrate-depletion approach with enantioselective quantification of substrate consumption by gas chromatography-negative ion chemical ionization mass spectrometry. SULT1A1 and SULT1A3 catalyzed sulfation of DHMA, and SULT1A3 and SULT1E1 catalyzed sulfation of HMMA. SULT1A1 and SULT1E1 revealed classic Michaelis-Menten kinetics, whereas SULT1A3 kinetics showed deviation from the typical Michaelis-Menten kinetics, resulting in a concentration-dependent self-inhibition. SULT1A3 showed the highest affinity and capacity of the SULT isoforms. Marked enantioselectivity could be observed for S-DHMA sulfation by SULT1A3 and in human liver cytosol, whereas no differences were observed for HMMA sulfation. Finally, comparison of Km and Vmax values calculated using achiral product formation and chiral substrate depletion showed good correlation within 2-fold of each other. In conclusion, preferences for S-enantiomers were observed for DHMA sulfation, but not for HMMA sulfation.

Use of fission yeast heterologously expressing human cytochrome P450 2B6 in biotechnological synthesis of the designer drug metabolite N-(1-phenylcyclohexyl)-2-hydroxyethanamine

Standards of drug metabolites are required for drug metabolism studies as a basis for toxicological risk assessment with respect to drug interactions and pharmacogenetic polymorphisms. They are further needed as reference compounds in analytical toxicology. However, metabolite standards are often not commercially available, particularly in the case of new designer drugs. As an alternative to often cumbersome chemical synthesis, human cytochrome P450 (CYP) isoenzymes heterologously expressed in the fission yeast Schizosaccharomyces pombe can be used for the biotechnological synthesis of drug metabolites. In the present study this concept was applied to the synthesis of N-(1-phenylcyclohexyl)-2-hydroxyethanamine (PCHEA), the common O-dealkyl metabolite of the designer drugs N-(1-phenylcyclohexyl)-2-methoxyethanamine (PCMEA) and N-(1-phenylcyclohexyl)-2-ethoxyethanamine (PCEEA). After adding 250 micromol PCEEA x HCl (62 mg), a 1 l culture of CAD65 (S. pombe strain co-expressing human CYP reductase and CYP2B6) was fermented over 65 h (pH 8, 30 degrees C) and centrifuged. PCHEA and remaining parent drug were isolated from the supernatant by solid-phase extraction (SPE). The eluate was evaporated to dryness and reconstituted in HPLC solvent. Aliquots were separated by semi-preparative HPLC. From the respective fraction, PCHEA was extracted by liquid-liquid extraction and precipitated as hydrochloric salt. Approximately 80% of PCEEA was converted to PCHEA. The final yield of PCHEA x HCl was 9 mg (35 micromol). Its identity was confirmed by GC-MS, (1)H NMR and (13)C NMR. The product purity, as determined by HPLC-UV, was 95%.

Investigations on the cytochrome P450 (CYP) isoenzymes involved in the metabolism of the designer drugs N-(1-phenyl cyclohexyl)-2-ethoxyethanamine and N-(1-phenylcyclohexyl)-2-methoxyethanamine

Investigations using insect cell microsomes with cDNA-expressed human cytochrome P450 (CYP)s and human liver microsomes (HLM) are reported on the CYP isoenzymes involved in the metabolism of the designer drugs N-(1-phenylcyclohexyl)-2-ethoxyethanamine (PCEEA) to O-deethyl PCEEA and N-(1-phenylcyclohexyl)-2-methoxyethanamine (PCMEA) to O-demethyl PCMEA. Gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry was used for the analysis of the incubation samples. PCEEA O-deethylation was catalyzed by CYP2B6, CYP2C9, CYP2C19, and CYP3A4, while PCMEA O-demethylation was catalyzed only by CYP2B6 and CYP2C19. Considering the relative activity factor approach, these enzymes accounted for 53%, 25%, 4%, and 18% of net clearance for PCEEA and 91% and 9% of net clearance for PCMEA, respectively. The chemical CYP2B6 inhibitor 4-(4-chlorobenzyl)pyridine (CBP) reduced the metabolite formation in pooled HLM by 63% at 1 microM PCEEA. At 10 microM PCEEA, CBP reduced metabolite formation by 61%, while inhibition of CYP3A4 by ketoconazole and inhibition of CYP2C9 by sulfaphenazole showed no inhibitory effect. At 1 microM PCMEA, CBP reduced metabolite formation in pooled HLM by 70% and at 10 microM PCMEA by 78%, respectively. In conclusion, the main metabolic step of both studied drugs was catalyzed by different CYPs.

Identification of cytochrome P450 enzymes involved in the metabolism of the designer drugs N-(1-phenylcyclohexyl)-3-ethoxypropanamine and N-(1-phenylcyclohexyl)-3-methoxypropanamine.

The involvement of human hepatic cytochrome P450 isoenzymes (P450s) in the metabolism of the designer drugs N-(1-phenylcyclohexyl)-3-ethoxypropanamine (PCEPA) and N-(1-phenylcyclohexyl)-3-methoxypropanamine (PCMPA) to the common metabolite N-(1-phenylcyclohexyl)-3-hydroxypropanamine (PCHPA) was studied using insect cell microsomes with cDNA-expressed human P450s and human liver microsomes (HLMs). Incubation samples were analyzed by gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry. Among the tested isoenzymes, P450 2B6, P450 2C19, P450 2D6, and P450 3A4 catalyzed PCEPA O-deethylation, and P450 2B6, P450 2C19, and P450 2D6 catalyzed PCMPA O-demethylation. According to the relative activity factor approach, these enzymes accounted for 22, 3, 30, and 45% of the net clearance for PCEPA and 51, 8, and 40% of the net clearance for PCMPA, respectively. At 1 microM PCEPA, the chemical inhibitors 4-(4-chlorobenzyl)pyridine for P450 2B6 and quinidine for P450 2D6 reduced metabolite formation in pooled HLMs by 37 and 73%, respectively, and at 10 microM PCEPA, they reduced metabolite formation by 57 and 26%, respectively. At 1 microM PCMPA, 4-(4-chlorobenzyl)pyridine and quinidine reduced metabolite formation in pooled HLMs by 25 and 39%, respectively, and at 10 microM PCMPA, they reduced metabolite formation by 62 and 27%, respectively. The experiments with the MAB inhibitory to P450 3A4 and the chemical inhibitor ketoconazole for P450 3A4 showed no inhibitory effect concerning PCEPA O-dealkylation. Experiments with HLMs from P450 2D6 poor metabolizers showed a reduction of metabolite formation as compared to pooled HLM of 73 and 25% (1 microM and 10 microM PCEPA) and 40 and 38% (1 microM and 10 microM PCMPA), respectively. In conclusion, the main metabolic step was catalyzed by different P450s.

Whole-cell biotransformation assay for investigation of the human drug metabolizing enzyme CYP3A7.

The cytochrome P450 isoform CYP3A7 (wildtype) is the major form of CYP in human fetal liver. Since it is not exclusively expressed in the fetus but also in a significant number of adults, CYP3A7 has been moving into the focus of investigation on adverse drug reactions and interindividual differences in drug metabolism in the last few years. In addition, CYP3A7 is overexpressed in hepatocellular carcinoma (HCC), where it contributes to the elimination of drugs. We here report the development of a convenient and reliable whole-cell system for testing CYP3A7 activity using recombinant fission yeast. As expected, catalytic properties of wild type CYP3A7.1 and its polymorphic form CYP3A7.2 towards DHEA and testosterone resembled those reported previously. Interestingly, both isoforms of CYP3A7 did not metabolize the anti-cancer drug sorafenib (which is approved for the treatment of HCC), while CYP3A4 produced the N-oxide in our system, as expected. This finding suggests that CYP3A7 activity does not influence the effectiveness of this anti-cancer drug against HCC. Furthermore, CYP3A7-expressing fission yeast cells specifically converted a luciferin-derivate (luciferin-PFBE) to a luminescent product and this activity can conveniently be monitored by spectrometry, which allowed the determination of IC₅₀-values for the broad-range P450 inhibitors econazole and miconazole, respectively. We believe that these new tools for a fast and easy investigation of substrates and inhibitors of human CYP3A7 will contribute to the gain of important insights for drug metabolism, efficacy and safety.