Determination of free serotonin and its metabolite 5-HIAA in blood human samples with consideration to pre-analytical factors.

Significant differences have been reported over the years in measuring physiological levels of free circulating serotonin (f5-HT) in platelet-poor plasma (PPP). This work shows that there are crucial pre-analytical factors in sample manipulation that can provoke an artifactual release of 5-HT from platelets, and that, even when the sample is accurately processed to obtain PPP, f5-HT levels are approximately 2.8 times higher than those of f5-HT in blood. An alternative methodology consisting of ex vivo blood microdialysis coupled to high-performance liquid chromatography-electrochemical detection is proposed and validated. It is considered the most accurate technique to measure physiological circulating f5-HT and its metabolite 5-hydroxyindoleacetic acid (f5-HIAA), owing to its sensitivity (limits of quantification of 0.08 ng/mL) and reliability since there is no sample manipulation. The f5-HT and f5-HIAA levels in blood and in PPP were studied in control subjects, hypertensive and end-stage renal disease patients, who have a deregulated serotonergic system. This work reveals that blood is the best matrix to determine f5-HT concentrations, and the clinical relevance of the accuracy of f5-HT determination is discussed.

Dose-Response Pharmacological Study of Mephedrone and Its Metabolites: Pharmacokinetics, Serotoninergic Effects, and Impact of CYP2D6 Genetic Variation.

Mephedrone (MEPH), the most widely consumed synthetic cathinone, has been associated with acute toxicity episodes. The aim of this report was to study its metabolic disposition and the impact of genetic variation of CYP2D6 on MEPH metabolism, in a dose range compatible with its recreational use. A randomized, crossover, phase I clinical trial was performed. Subjects received 50 and 100 mg (n = 3) and 150 and 200 mg (n = 6) of mephedrone and were genetically and phenotypically characterized for the CYP2D6 allelic variation. Our results showed a linear kinetics of mephedrone at the dose range assayed: plasma concentrations, cardiovascular and subjective effects, and blood serotonin concentrations all correlated in a dose-dependent manner. Mephedrone metabolic disposition is mediated by CYP2D6. Mephedrone pharmacology presented a linear dose-dependence within the range of doses tested. The metabolism of mephedrone by CYP2D6 implies that recreational users with no or low CYP2D6 functionality are exposed to unwanted acute toxicity episodes.

Changes in serotonin transporter (5-HTT) gene expression in peripheral blood cells after MDMA intake.

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is an amphetamine derivative abused worldwide. Although data report that relatively high doses of MDMA deplete serotonin (5-HT) content and decrease the availability of serotonin transporters (5-HTT), there is no available evidence as to the adaptive mechanisms taking place in 5-HTT gene expression following MDMA intake in humans. OBJECTIVE: To evaluate the pharmacological effects of MDMA on 5-HTT gene expression, using peripheral mononuclear cells as a biomarker of the central nervous system, and study whether an association exists between 5-HTT gene expression and psychobiological scores. METHODS: A randomized, double-blind, controlled trial was conducted in 18 (nine women) healthy recreational MDMA users. Subjects were genotyped for 5-HTT linked polymorphism region (5-HTTLPR). MDMA 75 mg or placebo was administered; Profile of Mood States (POMS) and 5-HTT gene expression measures were performed at baseline, 90, and 165 min post administration. POMS scores were correlated with changes in gene expression. RESULTS: The administration of 75 mg MDMA induced a significant twofold increase in 5-HTT gene expression after 165 min of drug administration. Significant associations were found between gene expression and POMS scores after MDMA administration. Results for each gender and 5-HTTLPR genotype are also reported. CONCLUSIONS: Preliminary results show that MDMA causes substantial regulatory changes in the expression of serotonergic markers, likely being modulated by the 5-HTTLPR polymorphism. Changes in 5-HTT gene expression may play an important role in the regulation of mood state.

No evidence that MDMA-induced enhancement of emotional empathy is related to peripheral oxytocin levels or 5-HT1a receptor activation.

The present study aimed at investigating the effect of MDMA on measures of empathy and social interaction, and the roles of oxytocin and the 5-HT1A receptor in these effects. The design was placebo-controlled within-subject with 4 treatment conditions: MDMA (75 mg), with or without pindolol (20 mg), oxytocin nasal spray (40 IU+16 IU) or placebo. Participants were 20 healthy poly-drug MDMA users, aged between 18-26 years. Cognitive and emotional empathy were assessed by means of the Reading the Mind in the Eyes Test and the Multifaceted Empathy Test. Social interaction, defined as trust and reciprocity, was assessed by means of a Trust Game and a Social Ball Tossing Game. Results showed that MDMA selectively affected emotional empathy and left cognitive empathy, trust and reciprocity unaffected. When combined with pindolol, these effects remained unchanged. Oxytocin did not affect measures of empathy and social interaction. Changes in emotional empathy were not related to oxytocin plasma levels. It was concluded that MDMA (75 mg) selectively enhances emotional empathy in humans. While the underlying neurobiological mechanism is still unknown, it is suggested that peripheral oxytocin does not seem to be the main actor in this; potential candidates are the serotonin 2A and the vasopressin 1A receptors. Trial registration: MDMA & PSB NTR 2636.

MDMA, methamphetamine, and CYP2D6 pharmacogenetics: what is clinically relevant?

In vitro human studies show that the metabolism of most amphetamine-like psychostimulants is regulated by the polymorphic cytochrome P450 isozyme CYP2D6. Two compounds, methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA), were selected as archetypes to discuss the translation and clinical significance of in vitro to in vivo findings. Both compounds were chosen based on their differential interaction with CYP2D6 and their high abuse prevalence in society. Methamphetamine behaves as both a weak substrate and competitive inhibitor of CYP2D6, while MDMA acts as a high affinity substrate and potent mechanism-based inhibitor (MBI) of the enzyme. The MBI behavior of MDMA on CYP2D6 implies that subjects, irrespective of their genotype/phenotype, are phenocopied to the poor metabolizer (PM) phenotype. The fraction of metabolic clearance regulated by CYP2D6 for both drugs is substantially lower than expected from in vitro studies. Other isoenzymes of cytochrome P450 and a relevant contribution of renal excretion play a part in their clearance. These facts tune down the potential contribution of CYP2D6 polymorphism in the clinical outcomes of both substances. Globally, the clinical relevance of CYP2D6 polymorphism is lower than that predicted by in vitro studies.

Effects of MDMA and related analogs on plasma 5-HT: relevance to 5-HT transporters in blood and brain.

(±)-3,4-Methylenedioxymethamphetamine (MDMA) is an illicit drug that evokes transporter-mediated release of serotonin (5-HT) in the brain. 5-HT transporter (SERT) proteins are also expressed in non-neural tissues (e.g., blood), and evidence suggests that MDMA targets platelet SERT to increase plasma 5-HT. Here we tested two hypotheses related to the effects of MDMA on circulating 5-HT. First, to determine if MDMA metabolites might contribute to actions of the drug in vivo, we used in vitro microdialysis in rat blood specimens to examine the effects of MDMA and its metabolites on plasma 5-HT. Second, to determine whether effects of MDMA on plasma 5-HT might be used as an index of central SERT activity, we carried out in vivo microdialysis in blood and brain after intravenous MDMA administration. The in vitro results show that test drugs evoke dose-related increases in plasma 5-HT ranging from two- to sevenfold above baseline, with MDMA and its metabolite, (±)-3,4-methylenedioxyamphetamine (MDA), producing the largest effects. The ability of MDMA and related analogs to elevate plasma 5-HT is correlated with their potency as SERT substrates in rat brain synaptosomes. The in vivo results reveal that MDMA causes concurrent increases in extracellular 5-HT in blood and brain, but there are substantial individual differences in responsiveness to the drug. Collectively, our findings indicate that MDMA and its metabolites increase plasma 5-HT by a SERT-dependent mechanism, and suggest the possibility that measures of evoked 5-HT release in blood may reflect central SERT activity.

Clinical pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"): the influence of gender and genetics (CYP2D6, COMT, 5-HTT).

UNLABELLED: The synthetic psychostimulant MDMA (± 3,4-methylenedioxymethamphetamine, ecstasy) acts as an indirect serotonin, dopamine, and norepinephrine agonist and as a mechanism-based inhibitor of the cytochrome P-450 2D6 (CYP2D6). It has been suggested that women are more sensitive to MDMA effects than men but no clinical experimental studies have satisfactorily evaluated the factors contributing to such observations. There are no studies evaluating the influence of genetic polymorphism on the pharmacokinetics (CYP2D6; catechol-O-methyltransferase, COMT) and pharmacological effects of MDMA (serotonin transporter, 5-HTT; COMT). This clinical study was designed to evaluate the pharmacokinetics and physiological and subjective effects of MDMA considering gender and the genetic polymorphisms of CYP2D6, COMT, and 5-HTT. A total of 27 (12 women) healthy, recreational users of ecstasy were included (all extensive metabolizers for CYP2D6). A single oral weight-adjusted dose of MDMA was administered (1.4 mg/kg, range 75-100 mg) which was similar to recreational doses. None of the women were taking oral contraceptives and the experimental session was performed during the early follicular phase of their menstrual cycle. Principal findings show that subjects reached similar MDMA plasma concentrations, and experienced similar positive effects, irrespective of gender or CYP2D6 (not taking into consideration poor or ultra-rapid metabolizers) or COMT genotypes. However, HMMA plasma concentrations were linked to CYP2D6 genotype (higher with two functional alleles). Female subjects displayed more intense physiological (heart rate, and oral temperature) and negative effects (dizziness, sedation, depression, and psychotic symptoms). Genotypes of COMT val158met or 5-HTTLPR with high functionality (val/val or l/*) determined greater cardiovascular effects, and with low functionality (met/* or s/s) negative subjective effects (dizziness, anxiety, sedation). In conclusion, the contribution of MDMA pharmacokinetics following 1.4 mg/kg MDMA to the gender differences observed in drug effects appears to be negligible or even null. In contrast, 5-HTTLPR and COMT val158met genotypes play a major role. TRIAL REGISTRATION: ClinicalTrials.gov NCT01447472.

Changes in CYP1A2 activity in humans after 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) administration using caffeine as a probe drug.

3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is a ring-substituted amphetamine widely used for recreational purposes. MDMA is predominantly O-demethylenated in humans by cytochrome P450 (CYP) 2D6, and is also a potent mechanism-based inhibitor of the enzyme. After assessing the inhibition and recovery of CYP2D6 in a previous study, the aim of this work was to study in humans the activity of CYP1A2 in vivo after CYP2D6 had been inhibited by MDMA, using caffeine as a probe drug. Twelve male and nine female recreational MDMA users were included. In session 1, 100 mg of caffeine was given at 0 h. In session 2, a 1.5 mg/kg MDMA dose (range 75-100 mg) was given at 0 h followed by a 100 mg dose of caffeine 4 h later. Aliquots of plasma were assayed for caffeine (137X) and paraxanthine (17X) and statistically significant differences were assessed with a one-way ANOVA. There were significant gender differences at basal condition, which persisted after MDMA administration. CYP1A2 activity was higher in both genders after drug administration, with an increase in 40% in females and 20% in males. Results show an increase in CYP1A2 activity when CYP2D6 is inhibited by MDMA in both genders, being more pronounced in females.

Sex differences in 3,4-methylenedioxymethamphetamine (MDMA; ecstasy)-induced cytochrome P450 2D6 inhibition in humans.

BACKGROUND AND OBJECTIVE: 3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is a ring-substituted amphetamine widely used for recreational purposes. MDMA is predominantly O-demethylenated in humans by cytochrome P450 (CYP) 2D6 and is also a potent mechanism-based inhibitor of the enzyme. This study assessed the inhibition and recovery half-life of CYP2D6 and CYP3A4 activity in female subjects by administering the probe drug dextromethorphan before and repeatedly after MDMA administration. These data were compared with the data obtained from a previous study in male subjects. STUDY DESIGN: Twelve healthy female subjects who were CYP2D6 extensive metabolizers participated as outpatients in two experimental sessions. Session 1 was conducted over 2 days and session 2 over 10 days, with a minimum of 3 days between sessions. In session 1, subjects received a single oral dose of dextromethorphan 30 mg. In session 2, a 1.5 mg/kg MDMA dose was given at 0 hours, followed at 4 hours by repeated 30 mg doses of dextromethorphan over the next 10 days. METHODS: Plasma concentration-time profiles and urinary recoveries of dextromethorphan and its metabolites dextrorphan (DOR), 3-methoxymorphinan (MM) and hydroxymorphinan-3-ol (HM) were measured. RESULTS: MDMA given prior to dextromethorphan resulted in a 10-fold increase in the dextromethorphan maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC), with corresponding decreases in DOR and HM pharmacokinetic parameters. The mean ± SD C(max) of MDMA was 188.8 ± 16.7 ng/mL, with a time to reach C(max) (t(max)) of 2.0 ± 0.4 hours and an AUC from 0 to 25 hours of 2645.2 ± 170.9 mg · h/mL. The urinary recovery of the dextromethorphan dose as dextromethorphan and its main metabolites was 25.4 ± 8.9% with no MDMA pretreatment versus 6.6 ± 1.1% after 1.5 mg/kg of MDMA (p = 0.0001). The metabolic ratio (MR) increased almost 60-fold from 0.018 ± 0.028 to 0.998 ± 0.932 after MDMA administration, with 100% of the subjects having a value greater than the antimode of 0.3 that signified the poor-metabolizer phenotype. Data analysis of results obtained in the present study compared with those from a previous study in male subjects showed significant differences in the dextromethorphan/DOR MR in the 0- to 8-hour (session 1) and 4- to 12-hour (session 2, post MDMA) collection periods (p = 0.032 and p = 0.01, respectively). CYP2D6 activity recovered after 10 days to 90% of baseline activity, with a recovery half-life of 36.6 ± 22.9 hours. Male subjects showed a shorter recovery half-life (27.6 ± 25.1 hours). The measurement of CYP3A4 activity indicated a non-significant increase in C(max) and AUC values of MM after drug intake, but urinary data reflected significant differences in dextromethorphan/MM MR in both sexes, although the difference was more pronounced in women. Dextromethorphan/MM MR increased almost 3-fold from baseline. DISCUSSION AND CONCLUSION: In women the pretreatment with MDMA resulted in a decrease in dextromethorphan clearance. CYP2D6 activity recovered after 10 days to 90% of baseline activity. Regarding CYP3A4 activity, there is an apparent decrease in its activity after MDMA use. In women, MDMA use has been associated with psychiatric symptoms and psychological problems that may require psychopharmacological treatment with antidepressant drugs, some of which are known CYP2D6 substrates. MDMA-induced mechanism-based inhibition of CYP2D6 is of relevance, and physicians should be advised to prescribe medications whose metabolic disposition is not regulated by CYP2D6.