In vivo effects of 3,4-methylenedioxymethamphetamine (MDMA) and its deuterated form in rodents: Drug discrimination and thermoregulation

This animal study (n=41) compared the hyperthermic side effects of MDMA (1.5 mg/kg) and a deuterium-substituted analogue d2-MDMA in rats and found that d2-MDMA produced increases in body temperature that were shorter-lasting and of lower magnitude compared to equivalent doses of MDMA.

Abstract

“Background: Recent clinical studies support the use of 3,4-methylenedioxymethamphetamine (MDMA) as an adjunct treatment for post-traumatic stress disorder (PTSD). Despite these promising findings, MDMA administration in controlled settings can increase blood pressure, heart rate, and body temperature. Previous studies indicate that O-demethylated metabolites of MDMA contribute to its adverse effects. As such, limiting the conversion of MDMA to reactive metabolites may mitigate some of its adverse effects and potentially improve its safety profile for therapeutic use.

Methods: We compared the interoceptive and hyperthermic effects of a deuterium-substituted form of MDMA (d2-MDMA) to MDMA using rodent drug discrimination and biotelemetry procedures, respectively.

Results: Compared to MDMA, d2-MDMA produced full substitution for a 1.5 mg/kg MDMA training stimulus with equal potency and effectiveness in the drug discrimination experiment. In addition, d2-MDMA produced increases in body temperature that were shorter-lasting and of lower magnitude compared to equivalent doses of MDMA. Last, d2-MDMA and MDMA were equally effective in reversing the hypothermic effects of the selective 5-HT2A/2C antagonist ketanserin.

Conclusion: These findings indicate that deuterium substitution of hydrogen at the methylenedioxy ring moiety does not impact MDMA’s interoceptive effects, and compared to MDMA, d2-MDMA has less potential for producing hyperthermic effects and likely has similar pharmacodynamic properties. Given that d2-MDMA produces less adverse effects than MDMA, but retains similar desirable effects that are thought to relate to the effective treatment of PTSD, additional investigations into its effects on cardiovascular functioning and pharmacokinetic properties are warranted.“

Authors: Michael D.Berquist, SebastianLeth-Petersen, Jesper LanggaardKristensen & William E.Fantegrossia

Summary

Recent clinical studies support the use of MDMA as an adjunct treatment for posttraumatic stress disorder. However, O-demethylated metabolites of MDMA contribute to its adverse effects.

MDMA has regained clinical attention as an adjunct pharmacotherapy to treat posttraumatic stress disorder (PTSD), but some volunteers report anxiety, jaw clenching, headaches, and increased sensitivity to cold after MDMA administration. Moreover, prolonged traumatic stress increases risk for developing hypertension and cardiovascular disease.

Future treatment strategies with MDMA may include more frequent and prolonged administrations, as well as efforts to reduce MDMA’s acute adverse effects and risks for developing toxicity, while retaining its desirable therapeutic effects.

Previous studies have shown that MDMA’s ring-opened phase I metabolites, 3,4-dihydroxymethamphetamine (HHMA) and 3,4-dihydroxyamphetamine (HHA), contribute to its acute and long-term adverse effects. Deuterium substitution may reduce the rate of MDMA metabolism into these phase I metabolites, and therefore reduce adverse effects following acute administration.

MDMA has complex effects at monoamine transporters and neurohormones, which may be why d2-MDMA retains its desirable therapeutic effects. To determine if d2-MDMA has a similar capacity to MDMA in reversing hypothermia in mice, we used a two-lever drug discrimination procedure in rats trained to discriminate 1.5 mg/kg MDMA from saline and then administered MDMA or d2-MDMA.

2.1. Drugs and chemicals

Racemic deuterated MDMA hydrochloride was prepared from CD2Cl2 and 3,4-dihydroxybenzaldehyde and dissolved in 0.9 % physiological saline. It was administered intraperitoneally to mice or rats in 10 ml/kg injection volumes.

2.2. Animals

Eight male Sprague-Dawley rats were pair housed in polycarbonate cages in corncob bedding in an Association for Assessment and Accreditation of Laboratory Animal Care-accredited facility. They were placed under a food-restricted diet and given ad libitum access to tap water. Thirty-three male NIH Swiss mice were housed in polycarbonate cages in corncob bedding and were given ad libitum feeding of standard rodent chow and tap water prior to any handling. All experiments were conducted during the animals’ light cycle.

2.3.1. Apparatus

Eight computer-operated standard rat operant conditioning chambers were used, each equipped with two retractable levers, a food pellet dispenser, a 28 V overhead house light, a clicker, and a tone generator.

2.3.2. Training procedures

Rats were trained to lever press for food pellets under a fixed ratio schedule of reinforcement. After establishing stimulus control on each lever, rats were injected with 0.9 % physiological saline or 1.5 mg/kg MDMA and placed into a darkened chamber for eight 20 min sessions.

Following errorless training, rats underwent discrimination training with both levers extending into the operant chamber. Rats were considered ready for substitution testing after achieving 4 out of 5 consecutive discrimination training sessions.

2.3.3. Stimulus substitution tests

Rats were subjected to stimulus substitution test sessions that were similar to discrimination training sessions except no food pellets were delivered and the sessions ended upon completion of the first FR 20 or 5 min, whichever occurred first.

2.4.1. Surgical procedures

All surgical procedures were similar to those previously reported. Mice were housed in polycarbonate cages in corncob bedding for 7 days after surgery to recover and acclimate to the testing room.

2.4.2. Biotelemetry procedures

Twelve mice were randomly assigned to d2-MDMA or MDMA treatment groups, and their body temperature and locomotor activity were recorded for 24 h. They received ascending doses of d2-MDMA or MDMA, spaced four days apart.

2.4.3. Ketanserin pretreatment experiment

Twenty-one mice were used for the ketanserin pretreatment experiment. They were randomly assigned to 5.6 mg/kg ketanserin + saline, 5.6 mg/kg ketanserin + 10, 32, or 56 mg/kg d2-MDMA, or 5.6 mg/kg ketanserin + 10, 32, or 56 mg/kg MDMA treatment conditions.

Mice were given ketanserin and then d2-MDMA for 120 min. They were monitored for temperature changes every 15 min.

2.5. Data analysis

Acquisition of drug stimulus discrimination was quantified by the number of discrimination training sessions required for each subject to have met criteria necessary to begin stimulus substitution testing. Stimulus substitution test results are expressed as mean (SE) percent MDMA-lever selection for each dose tested.

MDMA and d2-MDMA dose-effect curves were generated, and average ED50 values were compared using 95 % confidence intervals. Biotelemetry and ketanserin pretreatment experiments were performed, and two-factor analysis of variance (ANOVA) procedures were used to analyze the data.

3.1. Discriminative stimulus effects of d2-MDMA in rats

Two rats were removed from the study because they died due to factors unrelated to the experiment and the other failed to show reliable discrimination performance. MDMA and d2-MDMA produced full substitution in rats trained to discriminate 1.5 mg/kg MDMA from saline, and there were no differences in percent MDMA-lever selection between MDMA and d2-MDMA at any dose.

3.2. d2-MDMA and MDMA effects on body core temperature following ascending dose administration in mice

One mouse in the MDMA treatment group had faulty sensor, so its temperature data is excluded from all graphs and data analysis, but its locomotor data is retained. MDMA increased body core temperature more pronouncedly than d2-MDMA. MDMA-treated mice showed a significantly higher maximal core temperature and a longer duration of core temperature exceeding 39 °C after administration of 56 mg/kg compared to 56 mg/kg d2-MDMA. There was no difference in locomotor activity between treatment groups, however, there was a main effect of dose.

3.3. Capacity of d2-MDMA and MDMA to attenuate ketanserin-induced hypothermia in mice

Administration of MDMA or d2-MDMA reversed the hypothermic effects of 5.6 mg/kg ketanserin (ip), but there was a time-dependent increase in rectal temperature following administration of MDMA or d2-MDMA compared to saline-treated mice.

A two-factor ANOVA revealed a main effect of dose, but no effect of treatment or interaction between treatment and dose, and a statistically significant interaction between treatment and session time for the 5.6 mg/kg ketanserin + 56 mg/kg MDMA and d2-MDMA comparison.

4. Discussion

This study found that rats can discriminate 1.5 mg/kg MDMA using drug discrimination procedures, which is consistent with previous studies using 1.5 mg/kg MDMA and similar training criteria. Deuterium substitution at the methylenedioxy ring moiety of MDMA did not alter its interoceptive effects, and d2-MDMA did not reduce response rate compared to saline. However, d2-MDMA may retain the desirable subjective effects that are thought to relate to the effective treatment of PTSD.

We used biotelemetry to measure body core temperature and locomotor activity in mice. We found that d2-MDMA produced shorter-lasting and lower magnitude increases in core temperatures compared to equivalent doses of MDMA, suggesting a potential therapeutic window for d2-MDMA.

Deuterium substitution at the methylenedioxy ring does not alter the pharmacodynamic properties of MDMA at least at the serotonin transporter and/or serotonin receptors.

MDMA stimulates the release of hormones that may contribute to its therapeutic profile. Deuterium substitution may be a viable strategy for improving the tolerability and safety of pharmacotherapeutics, and may be a suitable alternative to MDMA for treating psychiatric problems.

5. Conclusions

d2-MDMA produced hyperthermic effects that were lower magnitude and shorter duration than MDMA, and elicited discriminative stimulus properties that were indistinguishable from equivalent doses of MDMA.