Interindividual differences in the clinical toxicity of 3,4-methylene-dioxymethamphetamine (MDMA) may result from alterations in drug-metabolizing enzymes, such as cytochrome P450 monooxygenases (CYPs), that are involved in the metabolism of MDMA 1,2 shown in Supplementary Fig. S1, Supplemental digital content 1, https://links.lww.com/FPC/B41.
Only limited controlled data are available on the pharmacogenetics/toxicogenetics of MDMA 2. The aim of the present study was to investigate the role of CYP2D6 in the PK of MDMA in a prospectively designed pooled analysis of eight double-blind, placebo-controlled, crossover studies in a total of 139 healthy individuals (methods shown in Supplemental digital content 1, https://links.lww.com/FPC/B41). This is the first study with a meaningful sample size and the inclusion of several individuals with relevantly impaired function. We also performed both genotyping and phenotyping and used genetic activity scores 3 for CYP2D6 activity classification.
We found that CYP2D6 activity significantly altered plasma MDMA levels up to 3 h after drug administration (i.e. during drug absorption/distribution), but not beyond 3 h (i.e. during drug elimination; Supplementary Table S1, Supplemental digital content 1, https://links.lww.com/FPC/B41, Fig. 1a and Supplementary Fig. S2c, Supplemental digital content 1, https://links.lww.com/FPC/B41). A significant main effect of the CYP2D6 genotype on the Cmax of MDMA was found (F2,136=4.19, P=0.02), with higher Cmax values in CYP2D6 poor metabolizers (PMs) compared with extensive metabolizers (EMs; P=0.049; Supplementary Fig. S1a, Supplemental digital content 1, https://links.lww.com/FPC/B41). The CYP2D6 activity score similarly altered the Cmax of MDMA (Supplementary Table S1 and Supplementary Fig. S2b, Supplemental digital content 1, https://links.lww.com/FPC/B41). MDMA area under the concentration–time curve up to 6 h (AUC6) values also varied across CYP2D6 genotype groups (F2,136=5.25, P<0.01), with PMs showing higher AUC6 values compared with EMs (P<0.01; Supplementary Fig. S2d, Supplemental digital content 1, https://links.lww.com/FPC/B41). MDMA AUC6 values also differed between genotype-based CYP2D6 activity groups (Supplementary Table S1 and Supplementary Fig. S2e, Supplemental digital content 1, https://links.lww.com/FPC/B41). The CYP 2D6 genotype altered the concentration–time curve of the minor active metabolite 3,4-methylene-dioxyamphetamine (MDA) (Fig. 1b). The Cmax and AUC6 of MDA varied across genotypes (F2,136=8.82, P<0.01, and F2,136=9.09, P<0.001, respectively), which were higher in PMs compared with intermediate metabolizers (IMs; P<0.001) and EMs (P<0.001; Supplementary Fig. S3a and d, Supplemental Digital Content 1, https://links.lww.com/FPC/B41). The Cmax and AUC6 of MDA were also higher in individuals with a CYP2D6 activity score of 0 compared with all of the other CYP2D6 activity groups (Supplementary Table S1 and Supplementary Fig. S2b, c, e, Supplemental digital content 1, https://links.lww.com/FPC/B41). The CYP2D6 genotype influenced the concentration–time curve of the inactive metabolite 4-hydroxy-3-methoxymethamphetamine (HMMA; Fig. 1c). The CYP2D6 genotype altered the Cmax and AUC6 of HMMA (F2,73=3.50, P=0.03 and 5.22, P<0.01; Supplementary Table S1 and Supplementary Fig. S4a and d, Supplemental digital content 1, https://links.lww.com/FPC/B41). Cmax and AUC6 of HMMA were higher in individuals with high CYP2D6 activity (activity score of 2) compared with individuals with low activity (activity score of 0.5; Supplementary Table S1 and Supplementary Fig. S4b, c, e, Supplemental digital content 1, https://links.lww.com/FPC/B41). The CYP2D6 genotype altered the unconjugated HMMA concentrations similar to those of HMMA (Supplementary Table S2 and Supplementary Fig. S5, Supplemental digital content 1, https://links.lww.com/FPC/B41). The CYP2D6 genotype altered the MDMA/HMMA Cmax and AUC6 ratios (F2,73=10.98 and 10.08, both P<0.001; Fig. 1d). CYP2D6 PMs had higher MDMA/HMMA Cmax and AUC6 ratios compared with IMs (P<0.01 and P<0.05) and EMs (both P<0.001; Fig. 1d, and Supplementary Fig. S6a and d, Supplemental digital content 1, https://links.lww.com/FPC/B41). Individuals with a CYP2D6 activity score of 2 had lower MDMA/HMMA Cmax and AUC6 ratios compared with individuals with activity scores of 0, 0.5, and 1 (Supplementary Table S1 and Supplementary Fig. S6b, c, e, Supplemental digital content 1, https://links.lww.com/FPC/B41). The effects of CYP2D6 on the biotransformation of MDMA to HMMA over time are also evident in the hysteresis plots in Supplementary Fig. S8, Supplemental digital content 1, https://links.lww.com/FPC/B41. A correlation was found between the AUC6 values of MDMA and MDA (Rs=0.18, P<0.05, N=139), indicating that higher MDMA levels resulted in higher MDA levels. In contrast, higher AUC6 values of MDMA were negatively correlated with those of HMMA (Rs=−0.33, P<0.01, N=76) or unconjugated HMMA (Rs=−0.39, P<0.001, N=124), consistent with the impaired conversion of MDMA into HMMA.
CYP2D6 activity influenced both the cardiovascular and the psychotropic responses to MDMA. Both the MDMA-induced blood pressure response and subjective drug effects increased more rapidly in genotype-based CYP2D6 PMs compared with IMs and EMs (Fig. 2), reflected by group differences early in time after MDMA administration, whereas maximal effects did not differ. Elevations in systolic blood pressure were greater in PMs compared with IMs (P=0.02) and EMs (P=0.01) at 0.6 h (F2,135=3.50, P=0.03) and also tended to be greater at 1 h (F2,135=2.49, P=0.09) after drug administration. Subjective ‘any drug effect’ ratings were higher in PMs compared with both IMs and EMs at 0.6 h (P<0.05). ‘Drug liking’ ratings were higher in PMs compared with both IMs and EMs at 0.6 h (P<0.001) and 1 h (P<0.01) and tended to be higher at 1.5 h. No effects of the CYP2D6 genotype were found on heart rate or body temperature. The MDMA/HMMA ratio at 0.6 h, which inversely reflects CYP2D6 activity, was associated with the MDMA-induced elevations in systolic blood pressure (Rs=0.41, P<0.001, N=76), any drug effect (Rs=0.42, P<0.001), and drug liking (Rs=0.40, P<0.001) at 0.6 h. The association remained significant for systolic blood pressure up to 1.5 h and for any drug effect and drug liking up to 4 and 6 h, respectively.
As expected, the CYP2D6 phenotype was associated with the CYP2D6 genotype. The DM/DX ratio in the group of PMs with an activity score 0 was significantly greater than in all of the other activity score groups, but these ratios did not differ between IMs and the different EM groups or within the EM groups (Supplementary Table S1 and Supplementary Fig. S9, Supplemental digital content 1, https://links.lww.com/FPC/B41). Despite some discordance between individual genotypes and phenotypes, the effects of the CYP2D6 genotype (Fig. 1) and the CYP2D6 phenotype (Supplementary Fig. S10, Supplemental digital content 1, https://links.lww.com/FPC/B41) groups on MDMA and metabolite plasma–time curves were very similar. Additional findings are presented in the Supplementary material, Supplemental digital content 1, https://links.lww.com/FPC/B41.
Taken together, the present study found an increase in MDMA exposure and more rapid increases in the cardiostimulant and psychotropic effects of MDMA in individuals with poor CYP2D6 function. The mean Cmax levels of MDMA in the seven CYP2D6 PMs in the present study were only 1.15 times higher than in 111 EMs, and differences in the PK or subjective and blood pressure responses to MDMA were only present in the first hour after MDMA administration. Thus, interindividual differences in CYP2D6 function have a small and transient effect on the plasma concentration of MDMA and its pharmacodynamic effects. These findings are consistent with the mechanism-based inhibition of CYP2D6 by MDMA, turning all individuals into functional CYP2D6 PMs within 1 h after MDMA administration 4,5. Consistent with our experimental data, a physiologically based PK model estimated that the absence of CYP2D6 function in PMs would increase MDMA Cmax levels by only 36% 4. Consistent with the findings in genetically impaired CYP2D6 PMs in the present study, the pharmacological inhibition of CYP2D6 function increased the Cmax and AUC values of MDMA by 15–20 and 10–30%, respectively 6,7. The mean HMMA AUC6 in CYP2D6 PMs was four times lower (24%) compared with EMs. This more pronounced effect of the CYP2D6 genotype on HMMA concentrations compared with MDMA concentrations could be clinically relevant because metabolites that are formed by CYP2D6, including HHMA and HMMA, have been implicated in MDMA-induced neurotoxicity and hepatotoxicity 8, hyponatremia, and hyperthermia 9. Low CYP2D6 activity was associated with higher MDA levels. Although CYP2D6 has been shown to be involved in the N-demethylation of MDMA to MDA in-vitro 10, individuals with low CYP2D6 function appear to produce more MDA because the main metabolic pathway of CYP2D6-mediated MDMA-HMMA conversion is less active, thus resulting in higher MDMA levels and compensatory MDA formation. Altogether, statistically significant but only moderate clinical effects of CYP2D6 genetics or pharmacological CYP2D6 inhibition on MDMA disposition were found, effects that are attributable to the self-inhibition of CYP2D6 and phenoconversion. CYP2D6 PMs were not overrepresented in fatalities associated with ecstasy 11. However, individuals may be at increased risk when more than one CYP system is genetically impaired or pharmacologically inhibited. Severe or fatal MDMA toxicity and high plasma exposure to MDMA were noted in cases of co-use with ritonavir, which blocks not only CYP2D6 but also CYP2B6 and CYP3A4. In fact, because CYP2D6 is inhibited by MDMA itself in all individuals, polymorphisms in other CYPs (e.g. CYP1A2, CYP2C19, and CYP2B6) and the pharmacological inhibition of CYP3A4 may actually be more clinically relevant than CYP2D6 genetics. Supporting this view, CYP1A2 function was shown to increase after MDMA administration in another study 12, which possibly compensated for the inhibition of CYP2D6 function by MDMA. We have assessed the effects of CYPA12, CYP2C19, and CYP2B6 polymorphisms on the PK of MDMA in this study and the findings will be published separately. There were no moderating effects of these polymorphisms on the effects of CYP2D6.
The present study has limitations. We analyzed a pooled sample of different studies and different doses and the different CYP2D6 activity groups were not equally represented across studies and dose groups. In addition, there were only seven PMs and all were in the high-dose group. However, an analysis of the high-dose group only produced similar results as the analysis of the total sample.
In conclusion, the present study evaluated the CP2D6 pharmacogenetics of the PK of an important recreational substance in a unique cohort that included a relatively large number of individuals and a wide spectrum of CYP functions, including CYP2D6 PMs. The study found only moderate increases in the plasma exposure to MDMA and its active metabolite MDA and a more rapid onset of associated blood pressure and psychotropic effects in individuals with poor CYP2D6 function. Although CYP2D6 PMs may be at increased risk for MDMA toxicity, the self-inhibition of CYP2D6 reduces the impact of the CYP2D6 genotype on MDMA PK.
This study was supported by the Swiss National Science Foundation (grant no. 320030_1449493).
Conflicts of interest
There are no conflicts of interest.
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