1
|
Wawro AM, Gajera CR, Baker SA, Leśniak RK, Fischer CR, Saw NL, Shamloo M, Montine TJ. Enantiomers of 2-methylglutamate and 2-methylglutamine selectively impact mouse brain metabolism and behavior. Sci Rep 2021; 11:8138. [PMID: 33854131 PMCID: PMC8047011 DOI: 10.1038/s41598-021-87569-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 03/31/2021] [Indexed: 12/15/2022] Open
Abstract
Imbalance of excitatory and inhibitory neurotransmission is implicated in a wide range of psychiatric and neurologic disorders. Here we tested the hypothesis that insertion of a methyl group on the stereogenic alpha carbon of l-Glu or l-Gln would impact the γ-aminobutyric acid (GABA) shunt and the glutamate-glutamine cycle. (S)-2-methylglutamate, or (S)-2MeGlu, was efficiently transported into brain and synaptosomes where it was released by membrane depolarization in a manner equivalent to endogenous l-Glu. (R)-2MeGlu was transported less efficiently into brain and synaptosomes but was not released by membrane depolarization. Each enantiomer of 2MeGlu had limited activity across a panel of over 30 glutamate and GABA receptors. While neither enantiomer of 2MeGlu was metabolized along the GABA shunt, (S)-2MeGlu was selectively converted to (S)-2-methylglutamine, or (S)-2MeGln, which was subsequently slowly hydrolyzed back to (S)-2MeGlu in brain. rac-2MeGln was also transported into brain, with similar efficiency as (S)-2MeGlu. A battery of behavioral tests in young adult wild type mice showed safety with up to single 900 mg/kg dose of (R)-2MeGlu, (S)-2MeGlu, or rac-2MeGln, suppressed locomotor activity with single ≥ 100 mg/kg dose of (R)-2MeGlu or (S)-2MeGlu. No effect on anxiety or hippocampus-dependent learning was evident. Enantiomers of 2MeGlu and 2MeGln show promise as potential pharmacologic agents and imaging probes for cells that produce or transport l-Gln.
Collapse
Affiliation(s)
- Adam M Wawro
- Department of Pathology, Stanford University, Stanford, USA
| | | | - Steven A Baker
- Department of Pathology, Stanford University, Stanford, USA
| | | | | | - Nay L Saw
- Behavioral and Functional Neuroscience Laboratory, Stanford University, Stanford, USA
| | - Mehrdad Shamloo
- Behavioral and Functional Neuroscience Laboratory, Stanford University, Stanford, USA.,Department of Neurosurgery, Stanford University, Stanford, USA
| | | |
Collapse
|
2
|
Zlatopolskiy BD, Endepols H, Krasikova RN, Fedorova OS, Ermert J, Neumaier B. 11C- and 18F-labelled tryptophans as PET-tracers for imaging of altered tryptophan metabolism in age-associated disorders. RUSSIAN CHEMICAL REVIEWS 2020. [DOI: 10.1070/rcr4954] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The ageing of the world’s population is the result of increased life expectancy observed in almost all countries throughout the world. Consequently, a rising tide of ageing-associated disorders, like cancer and neurodegenerative diseases, represents one of the main global challenges of the 21st century. The ability of mankind to overcome these challenges is directly dependent on the capability to develop novel methods for therapy and diagnosis of age-associated diseases. One hallmark of age-related pathologies is an altered tryptophan metabolism. Numerous pathological processes including neurodegenerative and neurological diseases like epilepsy, Parkinson’s and Alzheimer’s diseases, cancer and diabetes exhibit marked changes in tryptophan metabolism. Visualization of key processes of tryptophan metabolic pathways, especially using positron emission tomography (PET) and related hybrid methods like PET/CT and PET/MRI, can be exploited to early detect the aforementioned disorders with considerable accuracy, allowing appropriate and timely treatment of patients. Here we review the published 11C- and 18F-labelled tryptophans with respect to the production and also preclinical and clinical evaluation as PET-tracers for visualization of different branches of tryptophan metabolism.
The bibliography includes 159 references.
Collapse
|
3
|
Qiao Z, Mardon K, Stimson DHR, Migotto MA, Reutens DC, Bhalla R. Synthesis and evaluation of 6-[18F]fluoro-3-(pyridin-3-yl)-1H-indole as potential PET tracer for targeting tryptophane 2, 3-dioxygenase (TDO). Nucl Med Biol 2020; 84-85:1-10. [PMID: 31927462 DOI: 10.1016/j.nucmedbio.2019.12.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Revised: 12/17/2019] [Accepted: 12/17/2019] [Indexed: 12/19/2022]
Abstract
INTRODUCTION The increase in expression of tryptophan 2, 3-dioxygenases (TDO) and indoleamine 2,3-dioxygenase (IDO) have been reported as potential tumor biomarkers. TDO and IDO are enzymes that catalyze the first and rate-limiting step of the kynurenine pathway. Positron emitting tomography (PET) tracers investigating the kynurenine pathway may allow for the detection of different disease pathologies in vivo including cancer. However, current PET tracers being developed for TDO and IDO have suffered from either multi-step low yielding syntheses or de-fluorination of the tracer in vivo. RESULTS TDO inhibitors based on 6-fluoroindole with C3 substituents are a class of small molecules that have been shown to bind to TDO effectively, restore tryptophan concentration and decrease the production of immunosuppressive metabolites. The compound 6-fluoro-3-(pyridine-3-yl)-1H-indole has been reported to have high in vitro affinity for TDO. Herein we report the fully automated radiosynthesis of 6-[18F]fluoro-3-(pyridine-3-yl)-1H-indole [18F]4 using a copper-mediated nucleophilic 18F-fluorination resulting in a non-corrected yield of 5 to 6% of the tracer with a radiochemical purity of >99% after 4 h. Small animal dynamic PET/CT imaging of [18F]4 intravenously injected into normal C57BL/6 mice revealed rapid accumulation in heart and brain, reaching maximum occupancy in heart (10.9% ID/g) and brain (8.1% ID/g) at 1.75 min and 2.25 min, respectively. Furthermore, these in vivo studies revealed no de-fluorination of the tracer, as evidence by the absence of [18F]fluoride accumulation in bone. CONCLUSION In vitro studies demonstrate that 4 has good affinity for hTDO and the radiolabeled analogue [18F]4 can be synthesized with suitable radiochemical yields. [18F]4 demonstrates good uptake in the brain and the radiolabeled compound shows no de-fluorination in vivo in C57BL/6 mice.
Collapse
Affiliation(s)
- Zheng Qiao
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Karine Mardon
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia; National Imaging Facility, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Damion H R Stimson
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Mary-Anne Migotto
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - David C Reutens
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
| | - Rajiv Bhalla
- Centre for Advanced Imaging, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia.
| |
Collapse
|
4
|
Nordeman P, Yngve U, Wilking H, Gustavsson SÅ, Eriksson J, Antoni G. Automated GMP-production of α-[ 11 C]methyl-L-tryptophan using a tracer production system (TPS). J Labelled Comp Radiopharm 2018; 61:1106-1109. [PMID: 29902836 DOI: 10.1002/jlcr.3648] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2018] [Revised: 05/07/2018] [Accepted: 06/04/2018] [Indexed: 11/10/2022]
Abstract
The radiosynthesis and GMP validation of [11 C]AMT for human use are described. Three consecutive batches were produced giving 940-3790 MBq (4%-17% RCY, decay corrected, based on [11 C]CO2 ) of the tracer. The molar activity at the end of synthesis was 19 to 35 GBq/μmol, the radiochemical purity was ≥98%, and the enantiomeric purity was >99%. While the synthesis method was automated using a new generation of synthesis equipment, tracer production system developed in house, the method should be readily applicable to other synthesis platforms with minor modifications.
Collapse
Affiliation(s)
- Patrik Nordeman
- Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
| | - Ulrika Yngve
- Science for Life Laboratory, Drug Discovery and Development Platform, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
| | - Helena Wilking
- Uppsala University Hospital, PET-Centre, Uppsala, Sweden
| | | | - Jonas Eriksson
- Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
| | - Gunnar Antoni
- Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
| |
Collapse
|
5
|
Brain serotonin synthesis capacity in obsessive-compulsive disorder: effects of cognitive behavioral therapy and sertraline. Transl Psychiatry 2018; 8:82. [PMID: 29666372 PMCID: PMC5904107 DOI: 10.1038/s41398-018-0128-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/16/2017] [Revised: 01/06/2018] [Accepted: 01/31/2018] [Indexed: 02/01/2023] Open
Abstract
Cognitive behavioral therapy (CBT) and selective serotonin reuptake inhibitors (SSRIs) are both effective treatments for some patients with obsessive-compulsive disorder (OCD), yet little is known about the neurochemical changes related to these treatment modalities. Here, we used positron emission tomography and the α-[11C]methyl-L-tryptophan tracer to examine the changes in brain regional serotonin synthesis capacity in OCD patients following treatment with CBT or SSRI treatment. Sixteen medication-free OCD patients were randomly assigned to 12 weeks of either CBT or sertraline treatment. Pre-to-post treatment changes in the α-[11C]methyl-L-tryptophan brain trapping constant, K* (ml/g/min), were assessed as a function of symptom response, and correlations with symptom improvement were examined. Responders/partial responders to treatment did not show significant changes in relative regional tracer uptake; rather, in responders/partial responders, 12 weeks of treatment led to serotonin synthesis capacity increases that were brain-wide. Irrespective of treatment modality, baseline serotonin synthesis capacity in the raphe nuclei correlated positively with clinical improvement. These observations suggest that, for some patients, successful remediation of OCD symptoms might be associated with greater serotonergic tone.
Collapse
|
6
|
Skelin I, Fikre-Merid M, Diksic M. Both acute and subchronic treatments with pindolol, a 5-HT1A and β1 and β2 adrenoceptor antagonist, elevate regional serotonin synthesis in the rat brain: An autoradiographic study. Neurochem Int 2012; 61:1417-23. [DOI: 10.1016/j.neuint.2012.10.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2012] [Revised: 09/24/2012] [Accepted: 10/12/2012] [Indexed: 10/27/2022]
|
7
|
Eleventh international symposium on radiopharmaceutical chemistry: Abstracts. J Labelled Comp Radiopharm 2012. [DOI: 10.1002/jlcr.2580370701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
8
|
Berney A, Leyton M, Gravel P, Sibon I, Sookman D, Rosa Neto P, Diksic M, Nakai A, Pinard G, Todorov C, Okazawa H, Blier P, Nordahl TE, Benkelfat C. Brain regional α-[11C]methyl-L-tryptophan trapping in medication-free patients with obsessive-compulsive disorder. ACTA ACUST UNITED AC 2011; 68:732-41. [PMID: 21383250 DOI: 10.1001/archgenpsychiatry.2011.16] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
CONTEXT The hypothesis of a serotonin (5-hydroxytryptamine [5-HT]) dysfunction in obsessive-compulsive disorder (OCD) stems largely from the clinical efficacy of 5-HT reuptake inhibitors. Serotonergic abnormalities in the unmedicated symptomatic state, however, remain to be fully characterized. OBJECTIVE To investigate brain regional 5-HT synthesis, as indexed by positron emission tomography and the α-[(11)C]methyl-L-tryptophan trapping constant (K*), in treatment-free adults meeting criteria for OCD. DESIGN Between-group comparison. SETTING Department of Psychiatry and Montreal Neurological Institute, McGill University, and Department of Psychology, McGill University Health Centre, Quebec, Canada. PARTICIPANTS Twenty-one medication-free patients with OCD (15 men with a mean [SD] age of 33.2 [9.3] years and 6 women with a mean [SD] age of 35.8 [7.1] years) and 21 healthy controls matched for age and sex (15 men with a mean [SD] age of 32.9 [10.1] years and 6 women with a mean [SD] age of 36.5.5 [8.6] years). Main Outcome Measure The α-[(11)C]methyl-L-tryptophan brain trapping constant K*, which was analyzed with Statistical Parametric Mapping (SPM8) and with proportional normalization (extent threshold of 100 voxels with a peak threshold of P ≤ .005). RESULTS Compared with healthy controls, the patients with OCD exhibited significantly greater α-[(11)C]methyl-L-tryptophan trapping in the right hippocampus and left temporal gyrus (Brodmann area 20). In the larger subsample of all men, these same differences were also evident, as well as higher K* values in the caudate nucleus. Individual differences in symptom severity correlated positively with K* values sampled from the caudate and temporal lobe of the patients with OCD, respectively. There were no regions where the patients exhibited abnormally low K* values. Volumetric analyses found no morphometric alterations that would account for the group differences. CONCLUSION The results support previous reports of greater striatal and temporal lobe activity in patients with OCD than in healthy controls and suggest that these disturbances include a serotonergic component. Previously reported glucose metabolic disturbances in OCD involving the orbitofrontal and cingulate cortices, in comparison, might reflect postsynaptic changes in the serotonergic system.
Collapse
Affiliation(s)
- Alexandre Berney
- DERBH, Department of Psychiatry, McGill University, 1033 Pine Ave West, Montreal, QC H3A 1A1, Canada
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
9
|
XIIth international symposium on radiopharmaceutical chemistry: Abstracts and programme. J Labelled Comp Radiopharm 2010. [DOI: 10.1002/jlcr.2580401101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
10
|
Frey BN, Skelin I, Sakai Y, Nishikawa M, Diksic M. Gender differences in alpha-[(11)C]MTrp brain trapping, an index of serotonin synthesis, in medication-free individuals with major depressive disorder: a positron emission tomography study. Psychiatry Res 2010; 183:157-66. [PMID: 20630715 DOI: 10.1016/j.pscychresns.2010.05.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/14/2009] [Revised: 02/12/2010] [Accepted: 05/13/2010] [Indexed: 12/27/2022]
Abstract
Women are at higher risk than men for developing major depressive disorder (MDD), but the mechanisms underlying this higher risk are unknown. Here, we report proportionally normalized alpha-[(11)C]methyl-L-tryptophan brain trapping constant (alpha-[(11)C]MTrp K*(N)), an index of serotonin synthesis, in 25 medication-free individuals with MDD and in 25 gender- and age-matched healthy subjects who were studied using positron emission tomography (PET). Comparisons of alpha-[(11)C]MTrp K*(N) values between the men and women were conducted at the voxel and cluster levels using Statistical Parametric Mapping 2 (SPM2) analysis. In addition, the alpha-[(11)C]MTrp K*(N) values on both sides of the brain were extracted and compared to identify the left to right differences, as well as the gender differences. Women with MDD displayed higher alpha-[(11)C]MTrp K*(N) than men in the inferior frontal gyrus, anterior cingulate cortex (ACC), parahippocampal gyrus, precuneus, superior parietal lobule, and occipital lingual gyrus. In a matched group of normal subjects the gender differences were opposite from those found in MDD patients. Significant hemispheric differences in fronto-limbic structures between men and women with MDD were also observed. The K*(N) extracted from the volumes identified in MDD patients and in male and female normal subjects suggested no significant differences between males and females. In conclusion, depressed women have higher serotonin synthesis in multiple regions of the prefrontal cortex and limbic system involved with mood regulation, as compared with depressed men. Gender differences in brain serotonin synthesis may be related to higher risk for MDD in women.
Collapse
Affiliation(s)
- Benicio N Frey
- Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada H3A 2B4
| | | | | | | | | |
Collapse
|
11
|
Wadsak W, Mitterhauser M. Basics and principles of radiopharmaceuticals for PET/CT. Eur J Radiol 2010; 73:461-9. [PMID: 20181453 DOI: 10.1016/j.ejrad.2009.12.022] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Accepted: 12/15/2009] [Indexed: 11/28/2022]
Abstract
The presented review provides general background on PET radiopharmaceuticals for oncological applications. Special emphasis is put on radiopharmacological, radiochemical and regulatory aspects. This review is not meant to give details on all different PET tracers in depth but to provide insights into the general principles coming along with their preparation and use. The PET tracer plays a pivotal role because it provides the basis both for image quality and clinical interpretation. It is composed of the radionuclide (signaller) and the molecular vehicle which determines the (bio-)chemical properties (e.g. binding characteristics, metabolism, elimination rate).
Collapse
Affiliation(s)
- W Wadsak
- Department of Nuclear Medicine, Medical University of Vienna, Austria
| | | |
Collapse
|
12
|
Frey BN, Rosa-Neto P, Lubarsky S, Diksic M. Correlation between serotonin synthesis and 5-HT1A receptor binding in the living human brain: A combined α-[11C]MT and [18F]MPPF positron emission tomography study. Neuroimage 2008; 42:850-7. [DOI: 10.1016/j.neuroimage.2008.05.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2008] [Revised: 04/27/2008] [Accepted: 05/09/2008] [Indexed: 10/22/2022] Open
|
13
|
Sakai Y, Nishikawa M, Leyton M, Benkelfat C, Young SN, Diksic M. Cortical trapping of alpha-[(11)C]methyl-l-tryptophan, an index of serotonin synthesis, is lower in females than males. Neuroimage 2006; 33:815-24. [PMID: 16996279 DOI: 10.1016/j.neuroimage.2006.08.004] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Revised: 06/27/2006] [Accepted: 08/04/2006] [Indexed: 10/24/2022] Open
Abstract
One neural system that may exhibit gender differences is serotonin (5-HT), a neurotransmitter implicated in the regulation of mood, cognitive processes, and impulse-control. However, most of the available evidence of gender-related differences in this system has been indirect and at times contradictory. The objective of the present study was to follow up on preliminary evidence that there are gender differences in brain regional 5-HT synthesis, as measured by trapping of alpha-[(11)C]methyl-l-tryptophan (alpha-[(11)C]MTrp). Sixty-minute dynamic scans were performed in healthy volunteers, 28 women and 31 men. Functional images of the brain trapping constant, used as a proxy for 5-HT synthesis, which correlate in the rat brain with tryptophan's conversion into 5-HT, were transferred to the standardized 3D space. The voxel based comparison was performed by Statistical Parametric Mapping with proportional normalization. There was lower normalized alpha-[(11)C]MTrp trapping in females than males throughout much of the cerebral cortex, including the left middle frontal gyrus, the bilateral inferior frontal gyrus, the bilateral precentral gyrus, the left supramarginal gyrus, the bilateral inferior parietal lobule, the left superior temporal gyrus, the bilateral posterior cingulate gyrus, and the bilateral precuneus. There were no regions in which the normalized trapping was significantly higher in females than in males. Gender differences in sub-cortical sites were not found. Women, compared to men, may have lower rates of this tracer trapping, used as a proxy for 5-HT synthesis, throughout much of the cerebral cortex which is likely related to differences in 5-HT synthesis because relative differences in the normalized trapping should be the same as those in 5-HT synthesis. These differences may be related, at least in part, to previously suggested gender differences in affect, cognitive processes, and susceptibility to 5-HT-related neuropsychiatric and neurological disorders.
Collapse
Affiliation(s)
- Y Sakai
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, 3801 University St., Montreal, Canada QC H3A 2B4
| | | | | | | | | | | |
Collapse
|
14
|
Nishikawa M, Kumakura Y, Young SN, Fiset P, Vogelzangs N, Leyton M, Benkelfat C, Diksic M. Increasing blood oxygen increases an index of 5-HT synthesis in human brain as measured using alpha-[(11)C]methyl-L-tryptophan and positron emission tomography. Neurochem Int 2005; 47:556-64. [PMID: 16157418 DOI: 10.1016/j.neuint.2005.07.006] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Revised: 06/21/2005] [Accepted: 07/15/2005] [Indexed: 10/25/2022]
Abstract
The main objective of this investigation was to test the hypothesis that brain serotonin (5-HT) synthesis, as measured by trapping of alpha-[(11)C]methyl-L-tryptophan (alpha-MTrp) using positron emission tomography (PET), can be modulated by changes in blood oxygen. The study involved six healthy participants (three male and three female), who breathed a 15% or 60% oxygen mixture starting 15 min before the injection of tracer and continuing during the entire acquisition period. Participants were injected with up to 12m Ci of alpha-MTrp. Two sets of PET images were acquired while the participants were breathing each of the oxygen mixtures and, after reconstruction, all images were converted into brain functional images illustrating the brain trapping constant K(*) (microL/g/min). The K(*) values were obtained for 12 regions of interest outlined on the magnetic resonance images. The K(*) values obtained at high and low blood oxygen content were compared by paired statistics using Tukey's post hoc correction. As there were no difference in plasma tryptophan concentrations, these K(*) values are directly related to regional 5-HT synthesis. The results showed highly significant increases (50% on average) in brain serotonin synthesis (K(*) values) at high (mean value of 223+/-41 mmHg) relative to low (mean value 77.1+/-7.7 mmHg) blood oxygen levels. This suggests that tryptophan hydroxylase is not saturated with oxygen in the living human brain and that increases in blood oxygen can elevate brain serotonin synthesis.
Collapse
Affiliation(s)
- M Nishikawa
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, 3801 University St. Montreal, QC H3A2B4, Canada
| | | | | | | | | | | | | | | |
Collapse
|
15
|
Nakai A, Diksic M, Kumakura Y, D'Souza D, Kersey K. The effects of the 5-HT3 antagonist, alosetron, on brain serotonin synthesis in patients with irritable bowel syndrome. Neurogastroenterol Motil 2005; 17:212-21. [PMID: 15787942 DOI: 10.1111/j.1365-2982.2004.00615.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Serotonin (5-HT) plays an important role in the pathophysiology of irritable bowel syndrome (IBS). Using alpha-[(11)C]methyl-L-tryptophan-positron emission tomography (PET), it was demonstrated that brain 5-HT synthesis is increased in patients with IBS, in a gender-specific manner. The aims of the study were to evaluate the effects of alosetron on brain 5-HT synthesis in patients with IBS. Six male and five female non-constipation-predominant IBS patients were enrolled. The subjects received alosetron or a placebo for 14 days, separated by a 2-week washout period. On day 14, rectal distensions commenced just prior to the PET scan (which was performed for 80 min), and continued for 20-min periods. The functional images were analysed with SPM99. Alosetron vs placebo treatments, in a randomized, double-blinded, crossover manner, were studied. 5-HT synthesis was greater in several regions in the males than in the females during the alosetron treatment, whereas there was no region in which the females had greater synthesis. There were significant gender-treatment interactions of synthesis in the cingulate gyrus, caudate nucleus, globus pallidus, and cerebellum. The gender differences in the effect of alosetron on brain 5-HT synthesis may be related to the gender differences in the efficacy of alosetron.
Collapse
Affiliation(s)
- A Nakai
- McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, QC, Canada H3A2B4
| | | | | | | | | |
Collapse
|
16
|
Abstract
Factors that place constraints on radio-chemists who are seeking to design and develop radiopharmaceuticals for PET imaging studies include the short half-lives of 11C and 18F, minimum radiochemical yield and specific activity requirements, and high radiation fields that are associated with multi-Curie quantities of PET radionuclides. Nevertheless, during the past 20 years, considerable progress has been made in the development and application of a variety of PET radiotracers for a range of imaging studies in human subjects. We have highlighted a few areas of radiochemistry that focused on PET radiotracers that are described in this issue. Although the number of PET radiotracers synthesized is in the hundreds [6], much work remains to develop specific and useful PET radiotracers for a host of new and exciting noninvasive imaging applications.
Collapse
Affiliation(s)
- N Scott Mason
- Positron Emission Tomography Facility, Department of Radiology, University of Pittsburgh, B-938, UPMC Presbyterian, 200 Lothrop Street, Pittsburgh, PA 15213-2582, USA.
| | | |
Collapse
|
17
|
Nishizawa S, Leyton M, Okazawa H, Benkelfat C, Mzengeza S, Diksic M. Validation of a less-invasive method for measurement of serotonin synthesis rate with alpha-[11C]methyl-tryptophan. J Cereb Blood Flow Metab 1998; 18:1121-9. [PMID: 9778189 DOI: 10.1097/00004647-199810000-00009] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We tested in normal human subjects a less invasive method to obtain plasma input function required in the calculation of the brain serotonin synthesis rate measured with positron emission tomography (PET) and alpha-[11C]methyl-tryptophan (alpha-MTrp). The synthesis rates derived with the arterial input function were compared to those derived from venous plasma and venous sinus time-radioactivity curves obtained from dynamic PET images. Dynamic PET images were obtained for the lengths up to 90 minutes after an injection of alpha-MTrp (400 to 800 MBq). Input functions were generated from both artery and vein in three subjects, and from artery only in two subjects. Net unidirectional uptake constants of alpha-MTrp (K*; mL/g/min) were calculated in several brain regions graphically using data between 20 and 60 minutes after injection with different input functions. In the five subjects with arterial sampling, we tested two methods for correcting the input functions from the venous samples: (1) normalization to the mean exposure time at 20 minutes from arterial curve; and (2) the use of the venous sinus curve for the first 20 minutes. Venous curves coincided with the arterial ones after about 20 minutes. When the venous curves were used, there was an underestimation of the area under the curves up to 20 minutes, resulting in a 5% to 30% overestimation of K* values. Combined use of the sinus curve up to 20 minutes and venous curve from 20 to 60 minutes as an input function resulted in the K* (mL/g/min) values larger by 7.1 +/- 3.8% than the K* values estimated with the arterial input function. Normalization of the venous curve to the exposure time at 20 minutes obtained from the arterial plasma curve resulted in a bias in the K* of about -0.34 +/- 3.32%. The bias from the K* values was propagated to the serotonin synthesis rates. The use of a combination of the venous blood samples and venous sinus as the input function resulted in an acceptable bias in the serotonin synthesis rates from the tissue time-radioactivity curves generated by PET.
Collapse
Affiliation(s)
- S Nishizawa
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Quebec, Canada
| | | | | | | | | | | |
Collapse
|
18
|
Okazawa H, Diksic M. Image generation of serotonin synthesis rates using alpha-methyltryptophan and PET. J Comput Assist Tomogr 1998; 22:777-85. [PMID: 9754116 DOI: 10.1097/00004728-199809000-00021] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE We sought to create functional images of the serotonin (5-HT) synthesis rate obtained with alpha-[11C]methyl-L-tryptophan (alpha-MTrp) and PET and standardize them into the stereotaxic coordinate system. METHOD Dynamic PET scans were performed in 11 healthy subjects after an injection of alpha-MTrp. Results obtained by the Patlak plot and nonlinear least-squares methods using arterial plasma as input function were compared. The pixel-by-pixel calculation of functional images of 5-HT synthesis was done by the Patlak plot approach, after results were compared by two methods. Input function obtained by combining venous plasma and sinus radioactivities was also evaluated as an alternative to arterial input function. RESULTS There were no significant differences in 5-HT synthesis between the two calculation methods. The normalized venous input functions gave similar results as the arterial input function. The regional rates of 5-HT synthesis from functional images were not significantly different from those obtained by graphical plotting. CONCLUSION alpha-MTrp images could be converted into functional images representing 5-HT synthesis rates in the living brain, facilitating statistical comparison.
Collapse
Affiliation(s)
- H Okazawa
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Quebec, Canada
| | | |
Collapse
|
19
|
Nishizawa S, Benkelfat C, Young SN, Leyton M, Mzengeza S, de Montigny C, Blier P, Diksic M. Differences between males and females in rates of serotonin synthesis in human brain. Proc Natl Acad Sci U S A 1997; 94:5308-13. [PMID: 9144233 PMCID: PMC24674 DOI: 10.1073/pnas.94.10.5308] [Citation(s) in RCA: 623] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Rates of serotonin synthesis were measured in the human brain using positron emission tomography. The sensitivity of the method is indicated by the fact that measurements are possible even after a substantial lowering of synthesis induced by acute tryptophan depletion. Unlike serotonin levels in human brain, which vary greatly in different brain areas, rates of synthesis of the indolamine are rather uniform throughout the brain. The mean rate of synthesis in normal males was found to be 52% higher than in normal females; this marked difference may be a factor relevant to the lower incidence of major unipolar depression in males.
Collapse
Affiliation(s)
- S Nishizawa
- Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, H3A 2B4 Canada
| | | | | | | | | | | | | | | |
Collapse
|
20
|
Chakraborty PK, Mangner TJ, Chugani DC, Muzik O, Chugani HT. A high-yield and simplified procedure for the synthesis of alpha-[11C]methyl-L-tryptophan. Nucl Med Biol 1996; 23:1005-8. [PMID: 9004289 DOI: 10.1016/s0969-8051(96)00127-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Alpha-[11C]methyl-L-tryptophan (AMT) has been synthesized by stereoselective methylation with [11C]methyl iodide of the lithium-enolate generated by treating dimethyl 2(S), 3a(R), 8a(S)-(+)-hexahydro-8(phenylsulfonyl)pyrrolo [2, 3-b]indole-1,2-dicarboxylate (2) with lithium diisopropyl amide (LDA) at -55 degrees C, followed by ring opening using trifluoroacetic acid and alkaline hydrolysis of the protecting groups. The crude product was purified by a simple reverse-phase C-18 Sep-Pak procedure. The purified product was isolated with an average radiochemical yield of 53 +/- 12% (decay corrected) in 30-35 min from [11C]methyl iodide. At end of synthesis (EOS), 138 +/- 35 mCi (n = 24) of product was collected with a specific activity of ca. 1-1.3 Ci/mumol (EOS) (4-5 Ci/mumol @ EOB) starting from 1.5 Ci (EOB) of [11C]CO2.
Collapse
Affiliation(s)
- P K Chakraborty
- Children's Hospital of Michigan, Department of Pediatric Imaging, Wayne State University School of Medicine, Detroit 48201, USA
| | | | | | | | | |
Collapse
|
21
|
Diksic M, Grdisa M. Alpha-methyl-L-tryptophan as a tracer to study brain serotonergic system. Neurochem Res 1995; 20:1353-60. [PMID: 8786822 DOI: 10.1007/bf00992511] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- M Diksic
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Quebec, Canada
| | | |
Collapse
|