Investigation of Serotonin Neurotransmission in MDMA Users Using Combinated Dexfenfluramine Challenge and PET Imaging
Condition: Amphetamine-Related Disorders; Amphetamine Abuse
MeSH terms: Amphetamine-Related Disorders
Study type: Interventional

Summary: 
      Illicit use of the psychostimulant "Ecstasy" (3,4-methylenedioxymethamphetamine, MDMA) is
      considered a major public health issue. In Switzerland, MDMA and congeners are - after
      cannabis and cocaine - number three in the ranking of the most popular illicit drugs.
      Worldwide, Ecstasy is estimated to be even the second most popular illicit drug, used by
      millions of regular users.

      On the basis of animal data, it is likely that MDMA at high or cumulative doses damages
      serotonin (5-HT) neurons in the human brain. However, because of a multitude of
      methodological problems and a limited number of studies conducted in human subjects, no firm
      conclusions can yet be established whether chronic MDMA exposure produces a long lasting 5-HT
      deficiency syndrome, with consequent neuropsychiatric risks. To further address the putative
      neurotoxicity of MDMA in the human brain, we propose that novel functional assays of
      serotonergic neurotransmission may be useful to clarify this issue. We suggest that a 5-HT
      challenge study using positron emission tomography (PET) in conjunction with the 5-HT
      releaser dexfenfluramine [(+)FEN] may test the functional integrity of the 5-HT system in the
      living human brain.

      Specifically, in a placebo-controlled study, the 5-HT release capacity of serotonergic
      neurons shall be investigated by assessing [18F]-altanserin binding to 5-HT2A receptors
      following (+)FEN challenge in former and continuing MDMA users, and age and sex-matched
      MDMA-naïve controls. (+)FEN is a potent serotonin releaser without relevant affinity for
      5-HT, dopamine (DA) or norepinephrine (NE) receptors, and devoid of acute adverse effects in
      man. This makes (+)FEN an ideal pharmacological probe to explore functional integrity of
      serotonin neurotransmission.

      A second aim of our investigation is to detect possible impairments of cognitive functions
      and to study their relationship to serotonin neurotransmission as indexed by PET. In the
      course of the neuroimaging study, the investigators therefore also measure cognitive (e.g.
      attention, visual and working memory, learning, executive function) and affective functions
      (e.g. anxiety, impulsivity), suspected to be altered due to chronic MDMA use. Using
      correlational analyses, the investigators aim to determine if circumscribed regions of
      altered 5-HT function are associated with specific impairments in cognitive and/or
      behavioural parameters.

      We hypothesize that (+)FEN-evoked 5-HT release will discernibly alter availability of 5-HT2A
      receptors to [18F]-altanserin, with a pattern revealing the spatially heterogeneous
      vulnerability of 5-HT innervations to MDMA. The investigators predict that [18F]-altanserin
      volume of distribution (DV) will decline following (+)FEN challenge to a lesser extent in
      current MDMA users compared to MDMA-naïve control subjects. On the basis of animal data and
      recent neuroimaging studies in humans, the investigators hypothesize that functional recovery
      in former MDMA users will be manifest by a normalization or overshoot of the 5-HT release
      capacity.

      Our methodology will allow us to quantitatively assess serotonergic functions in the living
      human brain. The novel combination of (+)FEN-induced release of 5-HT from intracellular
      storage vesicles and subsequent PET assessment of competitively altered [18F]-altanserin
      binding at postsynaptic 5-HT2A receptors will provide a more direct biological marker of in
      vivo serotonin function than has been hitherto available. By applying this new
      pharmacological challenge/PET neuroimaging approach to groups of current and former users of
      MDMA, the investigators shall be able to gain important new insight in the debated functional
      consequences of MDMA use, especially concerning the controversy about the reversibility of
      5-HT changes following cessation of MDMA use. Successful completion of this project should
      have useful implications for public education and harm reduction with respect to MDMA use,
      and may also facilitate the development of possible treatment options for chronic MDMA users.
    

Detailed description: 
      Introduction: Illicit use of the psychostimulant 3,4-methylenedioxymethamphetamine (MDMA,
      "ecstasy") is considered a major public health issue. In Switzerland, the proportion of
      teenage MDMA users has increased continuously in recent years. According to a representative
      survey from 2002, approximately 3.3% of the 15-16 year old students in Switzerland have taken
      MDMA at least once. Compared with the corresponding data from 1994 (1.8%) and 1998 (1.9%),
      the increase of MDMA use among is evident. In another survey from the Swiss Institute for the
      Prevention of Alcoholism and Drug Addiction (SFA/ISPA) 2.2% of the anonymously interviewed
      subjects between 15 to 39 years reported experiences with MDMA. Also worldwide, MDMA has
      become one of the most widely used illegal psychoactive drugs, with millions of regular
      users.

      Acute administration of MDMA produces a rapid and marked release of serotonin (5-HT) via
      inhibition and reversal of the 5-HT transporter. Since the late 1980s, studies in non-human
      primates have provided convincing evidence that high doses of MDMA cause a substantial and
      sustained long-term neurotoxic loss of exclusively 5-HT nerve terminals with an associated
      depletion of up to 95% of 5-HT in several brain regions. In contrast, other neurotransmitter
      systems such as dopamine or norepinephrine remain undamaged. Subsequently, two studies with
      MDMA users have also shown selective decrements in cerebrospinal fluid (CSF) concentrations
      of 5-hydroxy indoleacetic acid, a marker for 5-HT depletion. In contrast, CSF concentrations
      of homovanillic acid or 3-methoxy-4-hydroxyphenylglycol, the major metabolites of dopamine
      and norepinephrine, were unchanged. Some imaging studies with serotonergic radioligands
      showed reduced 5-HT transporter (SERT) densities in cortical and subcortical brain regions of
      MDMA users. Moreover, electrophysiological studies have also suggested alterations of the
      5-HT system in regular users of MDMA. However, most of these findings in humans have been
      strongly criticised for methodological flaws (e.g. small sample sizes or lack of specificity
      of the applied radioligands). Consequently, there is as yet no convincing evidence for a
      selective serotonergic neurotoxicity of MDMA in humans. Moreover, the mechanism of MDMA
      neurotoxicity in animals is still under debate.

      In spite of these reservations, it has been consistently shown that MDMA users display
      dose-related impairments of verbal and visual-spatial memory, and impairments of executive
      functions and decision-making cognition. So far, the neuroanatomical basis of these
      neuropsychological deficits, and their relationship with 5-HT depletion, remain unclear.

      On the basis of animal data, it is likely that MDMA at high or cumulative doses damages 5-HT
      neurons in the human brain. However, because of a multitude of methodological problems and a
      limited number of studies conducted in human subjects, no firm conclusions can yet be
      established whether chronic MDMA exposure produces a long lasting 5-HT deficiency syndrome,
      with consequent neuropsychiatric risks. To further address the putative neurotoxicity of MDMA
      in the human brain, we propose that, in addition to the present receptor mapping studies,
      novel functional assays of serotonergic neurotransmission may be useful to clarify this
      issue. Specifically, we suggest that 5-HT challenge studies using positron emission
      tomography (PET) in conjunction with the serotonin releaser dexfenfluramine [(+)FEN] may test
      the functional integrity of the 5-HT system in the living human brain.

      Aims: To overcome impediments of previous imaging studies we propose to use a more direct
      approach to assess the integrity of serotonergic function in the human brain. 5-HT2A receptor
      mapping with PET and [18F]-altanserin, in combination with (+)FEN challenge, shall be used to
      investigate the 5-HT release capacity in current and former users of MDMA in comparison to
      drug-naïve control subjects.

      We anticipate that the comparison of changed specific binding of [18F]-altanserin to 5-HT2A
      receptors following (+)FEN-induced 5-HT release will reveal whether chronic abuse of MDMA
      leads to functional alterations in the human brain, and if MDMA users face an increased risk
      of developing a chronic serotonin deficiency syndrome, possibly associated with cognitive
      impairment and depression or anxiety. Our biological marker for 5-HT function in vivo shall
      enable us to topographically map regional 5-HT release, and hence to determine if the
      hypothesized 5-HT depletion has global or focal consequences for the action of (+)FEN. The
      putative functional consequences (affect regulation, cognition, and behaviour) can be linked
      to regions of reduced 5-HT transmission.

      By investigating current and former MDMA users, we shall assess the reversibility of 5-HT
      depletion. Furthermore, our (+)FEN challenge/PET imaging technique may reveal regions of
      increased 5-HT transmission due to hyperinnervation of 5-HT dendrites ("sprouting"), as
      occurs in MDMA-treated primates.

      In the course of the PET study, we shall also measure cognitive (e.g. attention, visual and
      working memory, learning, executive function) and affective functions (e.g. anxiety,
      impulsivity), suspected to be altered due to chronic MDMA use. Using correlational analyses,
      we aim to determine if circumscribed regions of altered 5-HT function are associated with
      specific impairments in cognitive and/or behavioural parameters.

      Current status of the project and pilot data: The radiosynthesis of the tracer
      [18F]-altanserin was established and validated according to GMP guidelines. The study and the
      use of (+)FEN and [18F]-altanserin has already been approved by the local ethics committee,
      Swissmedic and the Swiss Federal Office for Public Health (BAG). Furthermore, more than 50
      present and former MDMA users and 20 drug-naïve control subjects have been screened, and
      found to meet general inclusion criteria. We applied our method to four healthy human
      volunteers to prove our concept. The PET scans were metabolite corrected and normalised
      according to Logans graphical method. The regions of interest-based analysis was done with
      PMOD. We found that the apparent distribution volume (DV) of [18F]-altanserin was strongly
      decreased in all brain regions by about 11 to 15%. Thus, the proposed method is suitable to
      investigate 5-HT release capacity in humans.

      Working hypotheses: We hypothesize that (+)FEN-evoked 5-HT release will discernibly alter
      availability of 5-HT2A receptors to [18F]-altanserin, with a pattern revealing the spatially
      heterogeneous vulnerability of 5-HT innervations to MDMA. We predict that [18F]-altanserin DV
      will decline following (+)FEN challenge to a lesser extent in current MDMA users compared to
      MDMA-naïve control subjects. On the basis of animal data and recent neuroimaging studies in
      humans, we hypothesize that functional recovery in former MDMA users will be manifest by a
      normalization or overshoot of the serotonin release capacity.

      5-HT neurotransmission will not be homogeneously reduced in chronic MDMA users, but that
      toxic effects will be most evident in the frontal cortex and subcortical structures such as
      caudate nucleus and thalamus; these regions are innervated by fine fibers arising from the
      dorsal raphe nuclei that are especially sensitive to MDMA neurotoxicity in non-human
      primates. Based on results of recent human studies, we furthermore anticipate a dose-related
      impairment of cognitive functions, especially of memory and learning, as well as an increased
      state anxiety in current MDMA users, followed by improvement after cessation of drug use,
      although recovery may be incomplete. Finally, we hypothesize that the degree of impairment of
      cognitive functions will correlate significantly with the measured reduction of 5-HT
      function.

      Study design: To compare 5-HT neurotransmission in current MDMA users, former MDMA users, and
      MDMA-naïve control subjects, 16 subjects per group will be examined with [18F]-altanserin PET
      under two conditions. On two days - separated by an interval of 7 days - subjects will
      receive, in random order, placebo or 60 mg (+)FEN. Two hours later subjects will be
      positioned in the GE PET/CT with the head partially immobilized. Following acquisition of a
      low dose CT transmission scan, [18F]-altanserin (250 MBq, high specific activity) will be
      administered intravenously as a bolus over 30 sec, and dynamic PET data will be acquired
      during 90 minutes as a series of 36 frames increasing in duration from one minute to ten
      minutes. Subsequently, subjects will undergo a series of cognitive tasks from the Cambridge
      Neuropsychological Test Automated Battery (CANTAB). Moreover, potential affective reactions
      to the 5-HT release, anticipated group differences and the time course of affective reaction
      will be assessed by repeated use of psychometric questionnaires, specifically the State-Trait
      Anxiety Inventory (STAI), and Adjective Mood Rating Scale (AMRS). At intervals during the
      extended scanning and cognitive testing, venous blood samples will be collected for assay of
      (+)FEN, prolactin and cortisol concentrations by standard clinical procedures. The
      neuroendocrine responses will be correlated with the individual PET and neuropsychological
      test results.

      Subjects and screening procedure: Participants for the study are recruited by means of flyers
      distributed at locations associated with the "techno" and "rave" scene in Zurich, with the
      help of local associations involved in drug prevention/information and harm reduction.
      Experimental groups are matched for sex, age, and cannabis use. Sixteen subjects of both
      genders, aged 18 to 35, will be recruited for each of the following three experimental
      groups: 1) Current MDMA users (self-estimated lifetime use of ≥ 50 tablets of "Ecstasy", the
      last intake is dated back within the last 4 weeks), 2) former MDMA users (self-estimated
      lifetime use of ≥ 50 tablets, but subjects will have stopped using Ecstasy for at least one
      year prior inclusion), and 3) MDMA-naïve control subjects.

      Health of subjects will be determined by a general medical examination including
      electrocardiogram and standard laboratory parameters. To exclude subjects with current or
      past psychiatric conditions, all subjects will be assessed and diagnosed by a clinical
      psychologist using the SKID-I. During recruitments, potential subjects will be provided with
      extensive background information regarding administration of (+)FEN, neuropsychological
      testing, PET measures, and associated (radiation) risks, and will then be invited to give
      their written informed consent. Special liability is covered by hospital insurance for all
      subjects participating in this project. Pregnancy is an exclusion criterion; all female
      potential test subjects will have to agree to carry out a pregnancy test before entering the
      study.

      A detailed history of psychoactive drug use, including type of drugs, first and last use, and
      estimated total use will be recorded. All subjects will have to agree to abstain from using
      any psychoactive drug (except nicotine and cannabis) for at least two weeks before the first
      PET scan. At the beginning of each of the two experimental days, urine samples will be
      collected and screened for the presence of psychoactive drugs or metabolites.

      Relevance of the project: Our methodology will allow us to quantitatively assess serotonergic
      functions in the living human brain. The novel combination of (+)FEN-induced release of 5-HT
      from intracellular storage vesicles and subsequent PET assessment of competitively altered
      [18F]-altanserin binding at postsynaptic 5-HT2A receptors will provide a more direct
      biological marker of in vivo serotonin function than has been hitherto available. By applying
      this new pharmacological challenge/PET neuroimaging approach to groups of current and former
      users of MDMA, we shall be able to gain important new insight in the debated functional
      consequences of MDMA use, especially concerning the controversy about the reversibility of
      5-HT changes following cessation of MDMA use. The topographic mapping of regional 5-HT
      release following (+)FEN challenge in two groups of MDMA users and in a drug-naïve cohort
      will help to assess the contentious issue if chronic MDMA users face the risk of developing a
      global 5-HT deficiency syndrome, characterized by cognitive and affective changes. Successful
      completion of this project should have useful implications for public education and harm
      reduction with respect to MDMA use, and may also facilitate the development of possible
      treatment options for chronic MDMA users.
    

Intervention name(s): dexfenfluramine
Intervention type(s): Drug
Intervention description(s): oral, 40 mg to 60 mg, single application as a challenge
Other intervention name(s): d-fenfluramine; Benzeneethanamine; (S)-N-Ethyl-1-[3-(trifluoromethyl)phenyl]-propan-2-amine
Intervention MeSH terms: Fenfluramine; Dexfenfluramine
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: Ecstasy; MDMA; Serotonin; Neurotoxicity; dexfenfluramine; Positron emission tomography; altanserin; 5-HT2A receptor