Evaluation of [11C]Cimbi-36 as an Agonist PET Radioligand for Imaging of 5-HT2A Receptors
The serotonin 2A (5-HT2A) receptor is the most abundant excitatory serotonin (5-HT, 5-hydroxytryptamine) receptor in the human brain, and multiple positron emission tomography (PET) studies have investigated the 5-HT2A receptors in the human brain using antagonist radioligands. However, the currently available antagonist PET radioligands bind the total pool of 5-HT2A receptor receptors whereas a 5-HT2A receptor agonist binds the high-affinity subgroup of the receptors which are also G-protein coupled, and thus hypothesized to be the functional relevant population of receptors. At the Center for Integrated Molecular Brain Imaging (CIMBI), a novel agonist PET radioligands for brain imaging of 5-HT2A receptors was recently validated in animals (Ettrup et al. 2011, EJNMMI). In the human brain, [11C]Cimbi-36 was validated as a selective 5-HT2A receptor agonist PET radioligand through a blocking study with the 5-HT2A receptor antagonist pharmaceutical ketanserin. In this validation study, the biodistribution and kinetic modelling of [11C]Cimbi-36 binding in the human brain was also validated. With these studies, investigators will test the most promising of these, [11C]Cimbi-36, in clinical trials, where it will provide a novel method for detecting dysfunction in the 5-HT system. The specific aim of this clinical trial is:
- To examine the effect of acute alterations in 5-HT levels on cerebral [11C]Cimbi-36 binding in healthy volunteers who will be PET-scanned at baseline and after pharmacological or dietary interventions that either increase or decrease cerebral 5-HT levels.
It is hypothesized that this novel agonist radioligand will provide both a more physiological relevant measure of the 5-HT2A receptors and also reflect levels of cerebral 5-HT in humans, more specifically:
BP will decrease after pindolol and selective serotonin reuptake inhibitor (SSRI) treatment and increase after acute tryptophan depletion (ATD). Placebo will leave binding potential (BP) unchanged.
|Healthy||Drug: Citalopram and Pindolol Other: Placebo Dietary Supplement: Acute tryptophan depletion|
|Study Design:||Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Double Blind (Participant, Investigator, Outcomes Assessor)
Primary Purpose: Basic Science
|Official Title:||Evaluation of [11C]Cimbi-36 as an Agonist PET Radioligand for Imaging of 5-HT2A Receptors|
- Cerebral Cimbi-36 receptor binding in terms of binding potential (BP) at (1) baseline (2)acute tryptophan depletion (3) acute SSRI and pindolol (4) placebo [ Time Frame: 2 hours ]Cerebral Cimbi-36 receptor binding is measured with PET scanning for 2 hours. The resultant time-activity curves for brain tissue are used together with time-activity curves obtained with blood samples and kinetic modelling to yield unitless values of BP.
|Study Start Date:||January 2013|
|Study Completion Date:||November 2013|
|Primary Completion Date:||November 2013 (Final data collection date for primary outcome measure)|
Experimental: Citalopram and Pindolol
Citalopram intravenous infusion starting 30 min before scanning, 40 mg/h for 1 hour.
Pindolol peroral administration starting 3 days before scanning:
Day 1: 2.5 mg 3 times daily, day 2: 5 mg 3 times daily, day 3: 7.5 mg 3 times daily, Day 4 (scan day) 7.5 mg morning and noon.
Drug: Citalopram and Pindolol
Citalopram: selective serotonin reuptake inhibitor
Pindolol: non-selective beta blocker and 5-HT1A receptor antagonist
Placebo Comparator: Placebo
Placebo for pindolol: sugar tablets that resembles pindolol
Placebo for ATD: amino acid drink balanced formula (containing tryptophan)
Placebo for Seropram: NaCl infusion
On the second PET scanning day, subjects received a protein drink as well as a 50 ml saline infusion over 1 hour starting 30 min before PET scanning.
Experimental: Acute tryptophan depletion
Amino acid drink without tryptophan. Ingested 4-5 hours prior to PET scanning.
Dietary Supplement: Acute tryptophan depletion
Other Name: Amino acid drink without tryptophan
Please refer to this study by its ClinicalTrials.gov identifier: NCT01778686
|Neurobiology Research Unit, Rigshospitalet|
|Copenhagen, Denmark, 2100|