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A Survey of Molecular Imaging of Opioid Receptors. Molecules 2019; 24:molecules24224190. [PMID: 31752279 PMCID: PMC6891617 DOI: 10.3390/molecules24224190] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 11/11/2019] [Accepted: 11/13/2019] [Indexed: 01/09/2023] Open
Abstract
The discovery of endogenous peptide ligands for morphine binding sites occurred in parallel with the identification of three subclasses of opioid receptor (OR), traditionally designated as μ, δ, and κ, along with the more recently defined opioid-receptor-like (ORL1) receptor. Early efforts in opioid receptor radiochemistry focused on the structure of the prototype agonist ligand, morphine, although N-[methyl-11C]morphine, -codeine and -heroin did not show significant binding in vivo. [11C]Diprenorphine ([11C]DPN), an orvinol type, non-selective OR antagonist ligand, was among the first successful PET tracers for molecular brain imaging, but has been largely supplanted in research studies by the μ-preferring agonist [11C]carfentanil ([11C]Caf). These two tracers have the property of being displaceable by endogenous opioid peptides in living brain, thus potentially serving in a competition-binding model. Indeed, many clinical PET studies with [11C]DPN or [11C]Caf affirm the release of endogenous opioids in response to painful stimuli. Numerous other PET studies implicate μ-OR signaling in aspects of human personality and vulnerability to drug dependence, but there have been very few clinical PET studies of μORs in neurological disorders. Tracers based on naltrindole, a non-peptide antagonist of the δ-preferring endogenous opioid enkephalin, have been used in PET studies of δORs, and [11C]GR103545 is validated for studies of κORs. Structures such as [11C]NOP-1A show selective binding at ORL-1 receptors in living brain. However, there is scant documentation of δ-, κ-, or ORL1 receptors in healthy human brain or in neurological and psychiatric disorders; here, clinical PET research must catch up with recent progress in radiopharmaceutical chemistry.
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Harada N, Ohba H, Kakiuchi T, Tsukada H. Application of feedback-controlled bolus plus infusion (FC-B/I) method for quantitative PET imaging of dopamine transporters with [(18)F]β-CFT-FE in conscious monkey brain. Synapse 2012; 67:42-50. [PMID: 23042662 DOI: 10.1002/syn.21614] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Accepted: 10/03/2012] [Indexed: 01/03/2023]
Abstract
The competitive inhibition of dopamine transporters (DAT) with cocaine, a specific DAT inhibitor, was evaluated with a feedback-controlled bolus plus infusion (FC-B/I) method using animal positron emission tomography (PET) in the living brain of conscious monkey. 2β-Carbomethoxy-3β-(4-fluorophenyl)-8-(2-[(18)F]fluoroethyl) nortropane ([(18)F]β-CFT-FE; Harada et al. [2004] Synapse 54:37-45) was used for this study because it provided specific, fast, and reversible kinetic properties to DAT in the striatum. In FC-B/I method, the real-time image reconstruction was started just after intravenous bolus injection of [(18)F]β-CFT-FE to generate a time-activity curve in the striatum, and the infusion rate was adjusted to achieve an equilibrium state of the striatal radioactivity concentrations by means of a feedback-control algorithm. The first equilibrium state in the brain was reached within 20 min after the infusion start. Intravenous administration of cocaine at the doses of 0.02, 0.1, and 0.5 mg/kg shifted the equilibrium radioactivity level to the second equilibrium state in a dose-dependent manner, while no significant alterations was observed in the cerebellum. The present results demonstrated that the combined use of FC-B/I method and PET probe with fast kinetics like [(18)F]β-CFT-FE could be useful to assess the occupancy of drugs in the living brain with PET.
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Affiliation(s)
- Norihiro Harada
- Central Research Laboratory, Hamamatsu Photonics KK, 5000 Hirakuchi, Hamakita, Hamamatsu, Shizuoka 434-8601, Japan
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Kuwabara H, McCaul ME, Wand GS, Earley CJ, Allen RP, Weerts EM, Dannals RF, Wong DF. Dissociative changes in the Bmax and KD of dopamine D2/D3 receptors with aging observed in functional subdivisions of the striatum: a revisit with an improved data analysis method. J Nucl Med 2012; 53:805-12. [PMID: 22492734 DOI: 10.2967/jnumed.111.098186] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED Separate measurements of B(max), the density of available receptors, and K(D), the equilibrium dissociation constant in the human brain, with PET have contributed to our understanding of neuropsychiatric disorders, especially with respect to the dopamine D(2)/D(3) receptor system. However, existing methods have limited applications to the whole striatum, putamen, or caudate nucleus. Improved methods are required to examine B(max) and K(D) in detailed functional striatal subdivisions that are becoming widely used. METHODS In response, a new method (bolus-plus-infusion transformation [BPIT]) was developed. After completion of a validation study for (11)C-raclopride scans involving 81 subjects, age-associated changes in B(max) and K(D) were examined in 47 healthy subjects ranging in age from 18 to 77 y. RESULTS The BPIT method was consistent with established reference tissue methods regarding regional binding potential. BPIT yielded time-consistent estimates of B(max) and K(D) when scan and infusion lengths were set equal in the analysis. In addition, BPIT was shown to be robust against PET measurement errors when compared with a widely accepted transient equilibrium method. Altogether, BPIT was supported as a method for regional binding potential, B(max), and K(D). We demonstrated age-associated declines in B(max) in all 5 functional striatal subdivisions with BPIT when corrected for multiple comparisons. These age-related effects were not consistently attainable with the transient equilibrium method. Irrespective to methods, K(D) remained unchanged with age. CONCLUSION The BPIT approach may be useful for understanding dopamine receptor abnormalities in neuropsychiatric disorders by enabling separate measurements of B(max) and K(D) in functional striatal subdivisions.
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Affiliation(s)
- Hiroto Kuwabara
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
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Buprederm™, a New Transdermal Delivery System of Buprenorphine: Pharmacokinetic, Efficacy and Skin Irritancy Studies. Pharm Res 2008; 25:1052-62. [DOI: 10.1007/s11095-007-9470-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2007] [Accepted: 10/04/2007] [Indexed: 10/22/2022]
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Affiliation(s)
- R G Blasberg
- Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY, USA.
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van Dyck CH, Soares JC, Tan PZ, Staley JK, Baldwin RM, Amici LA, Fu X, Garg PK, Seibyl JP, Charney DS, Innis RB. Equilibrium modeling of 5-HT(2A) receptors with [18F]deuteroaltanserin and PET: feasibility of a constant infusion paradigm. Nucl Med Biol 2000; 27:715-22. [PMID: 11150702 DOI: 10.1016/s0969-8051(00)00160-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
[(18)F]Altanserin has emerged as a promising positron emission tomography (PET) ligand for serotonin-2A (5-HT(2A)) receptors. The deuterium substitution of both of the 2'-hydrogens of altanserin ([(18)F]deuteroaltanserin) yields a metabolically more stable radiotracer with higher ratios of parent tracer to radiometabolites and increased specific brain uptake than [(18)F]altanserin. The slower metabolism of the deuterated analog might preclude the possibility of achieving stable plasma and brain activities with a bolus plus constant infusion within a reasonable time frame for an (18)F-labeled tracer (T(1/2) 110 min). Thus, the purpose of this study was to test the feasibility in human subjects of a constant infusion paradigm for equilibrium modeling of [(18)F]deuteroaltanserin with PET. Seven healthy male subjects were injected with [(18)F]deuteroaltanserin as a bolus plus constant infusion lasting 10 h postinjection. PET acquisitions and venous blood sampling were performed throughout the infusion period. Linear regression analysis revealed that time-activity curves for both specific brain uptake and plasma [(18)F]deuteroaltanserin concentration stabilized after about 5 h. This permitted equilibrium modeling and estimation of V(')(3) (ratio of specific uptake to total plasma parent concentration) and the binding potential V(3) (ratio of specific uptake to free plasma parent concentration). Cortical/cerebellar ratios were increased by 26% relative to those we previously observed with [(18)F]altanserin using similar methodology in a somewhat older subject sample. These results demonstrate feasibility of equilibrium imaging with [(18)F]deuteroaltanserin and suggest that it may be superior to [(18)F]altanserin as a PET radioligand.
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Affiliation(s)
- C H van Dyck
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
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Abstract
Several groups have provided evidence that positron emission tomography (PET) and single-photon emission computed tomography (SPECT) neuroreceptor imaging techniques might be applied to measure acute fluctuations in dopamine (DA) synaptic concentration in the living human brain. Competition between DA and radioligands for binding to D2 receptor is the principle underlying this approach. This new application of neuroreceptor imaging provides a dynamic measurement of neurotransmission that is likely to be informative to our understanding of neuropsychiatric conditions. This article reviews and discusses the body of data supporting the feasibility and potential of this imaging paradigm. Endogenous competition studies performed in rodents, nonhuman primates, and humans are first summarized. After this overview, the validity of the model underlying the interpretation of these imaging data is critically assessed. The current reference model is defined as the occupancy model, since changes in radiotracer binding potential (BP) are assumed to be directly caused by changes in occupancy of D2 receptors by DA. Experimental data supporting this model are presented. The evidence that manipulation of DA synaptic levels induces change in the BP of several D2 radiotracers (catecholamines and benzamides) is unequivocal. The fact that these changes in BP are mediated by changes in DA synaptic concentration is well documented. The relationship between the magnitude of BP changes measured with PET or SPECT and the magnitude of changes in DA concentration measured by microdialysis supports the use of these noninvasive techniques to measure changes in neurotransmission. On the other hand, several observations remain unexplained. First, the amphetamine-induced changes in the BP of D2 receptor antagonists [123I]IBZM and [11C]raclopride last longer than amphetamine-induced changes in DA extracellular concentration. Second, nonbenzamide D2 receptor antagonists, such as spiperone and pimozide, are not affected by changes in DA release, or are affected in a direction opposite to that predicted by the occupancy model. Similar observations are reported with D1 radiotracers. These results suggest that the changes in BP following changes in DA concentration might not be fully accounted by a simple occupancy model. Specifically, the data are reviewed supporting that agonist-mediated receptor internalization might play an important role in characterizing receptor-ligand interactions. Finally, it is proposed that a better understanding of the mechanism underlying the effects observed with benzamides is essential to develop this imaging technique to other receptor systems.
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Affiliation(s)
- M Laruelle
- Department of Psychiatry and Radiology, Columbia University College of Physicians and Surgeons and New York State Psychiatric Institute, New York 10032, USA
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Koeppe RA, Frey KA, Kuhl DE, Kilbourn MR. Assessment of extrastriatal vesicular monoamine transporter binding site density using stereoisomers of [11C]dihydrotetrabenazine. J Cereb Blood Flow Metab 1999; 19:1376-84. [PMID: 10598942 DOI: 10.1097/00004647-199912000-00011] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Previous studies have demonstrated the utility of [11C]dihydrotetrabenazine ([11C]DTBZ) as a ligand for in vivo imaging of the vesicular monoamine transporter system. The (+)-isomer has a high affinity (approximately 1 nmol/L) for the vesicular monoamine transporter (VMAT2) binding site, whereas the (-)-isomer has an extremely low affinity (approximately 2 micromol/L). Efforts to model dynamic (+)-[11C]DTBZ data demonstrate the difficulty in separating the specific binding component from the free plus nonspecific component of the total positron emission tomography (PET) measure. The authors' previous PET work, as well as in vitro studies, indicate that there is little specific VMAT2 binding in neocortical regions. However, precise determination of in vivo binding levels have not been made, leaving important questions unanswered. At one extreme, is there sufficient specific binding in cortex or other extrastriate regions to be estimated reliably with PET? At the other extreme, is there sufficiently little binding in cortex so that it can be used as a reference region representing nonsaturable tracer uptake? The authors address these questions using paired studies with both active (+) and inactive (-) stereoisomers of [11C]DTBZ. Six normal control subjects were scanned twice, 2 hours apart, after injections of 16 mCi of (+)- and (-)-[11C]DTBZ (order counter-balanced). Three-dimensional PET acquisition consisted of 15 frames over 60 minutes for each scan. Arterial samples were acquired throughout, plasma counted, and corrected for radiolabeled metabolites. Analysis of specific binding was assessed by comparison of total distribution volume measures from the (+)- and (-)-[11C]DTBZ scans. The authors' findings indicate that only approximately 5% of the cortical signal in (+)-[11C]DTBZ scans results from binding to VMAT2 sites. The strongest extrastriatal signal comes from the midbrain regions where approximately 30% of the PET measure results from specific binding. The authors conclude that (1) the density of VMAT2 binding sites in cortical regions is not high enough to be quantified reliably with DTBZ PET, and (2) binding does appear to be low enough so that cortex can be used as a free plus nonspecific reference region for striatum.
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Affiliation(s)
- R A Koeppe
- Department of Internal Medicine, University of Michigan, Ann Arbor 48109, USA
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Stegman LD, Rehemtulla A, Beattie B, Kievit E, Lawrence TS, Blasberg RG, Tjuvajev JG, Ross BD. Noninvasive quantitation of cytosine deaminase transgene expression in human tumor xenografts with in vivo magnetic resonance spectroscopy. Proc Natl Acad Sci U S A 1999; 96:9821-6. [PMID: 10449778 PMCID: PMC22294 DOI: 10.1073/pnas.96.17.9821] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Analysis of transgene expression in vivo currently requires destructive and invasive molecular assays of tissue specimens. Noninvasive methodology for assessing the location, magnitude, and duration of transgene expression in vivo will facilitate subject-by-subject correlation of therapeutic outcomes with transgene expression and will be useful in vector development. Cytosine deaminase (CD) is a microbial gene undergoing clinical trials in gene-directed enzyme prodrug gene therapy. We hypothesized that in vivo magnetic resonance spectroscopy could be used to measure CD transgene expression in genetically modified tumors by directly observing the CD-catalyzed conversion of the 5-fluorocytosine (5-FC) prodrug to the chemotherapeutic agent 5-fluorouracil (5-FU). The feasibility of this approach is demonstrated in subcutaneous human colorectal carcinoma xenografts in nude mice by using yeast CD (yCD). A three-compartment model was used to analyze the metabolic fluxes of 5-FC and its metabolites. The rate constants for yCD-catalyzed prodrug conversion (k(1)(app)), 5-FU efflux from the observable tumor volume (k(2)(app)), and formation of cytotoxic fluorinated nucleotides from 5-FU (k(3)(app)) were 0.49 +/- 0.27 min(-1), 0.766 +/- 0.006 min(-1), and 0.0023 +/- 0.0007 min(-1), respectively. The best fits of the 5-FU concentration data assumed first-order kinetics, suggesting that yCD was not saturated in vivo in the presence of measured intratumoral 5-FC concentrations well above the in vitro K(m). These results demonstrate the feasibility of using magnetic resonance spectroscopy to noninvasively monitor therapeutic transgene expression in tumors. This capability provides an approach for measuring gene expression that will be useful in clinical gene therapy trials.
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Affiliation(s)
- L D Stegman
- Department of Radiology and Biological Chemistry, University of Michigan Medical School, 1150 West Medical Center Drive, MSRBIII Room 9301 Ann Arbor, MI 48109-0648, USA
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Ito H, Hietala J, Blomqvist G, Halldin C, Farde L. Comparison of the transient equilibrium and continuous infusion method for quantitative PET analysis of [11C]raclopride binding. J Cereb Blood Flow Metab 1998; 18:941-50. [PMID: 9740097 DOI: 10.1097/00004647-199809000-00003] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Several approaches have been applied for quantification of D2 dopamine receptors in positron emission tomography studies using [11C]raclopride. Initial approaches were based on analyses of data obtained after rapid bolus injection of [11C]raclopride. A continuous infusion paradigm has more recently been applied. The current study compares these approaches in healthy men. Two positron emission tomography measurements were performed in each of six healthy men, the first with rapid bolus injection and the second with continuous infusion of [11C]raclopride. In rapid bolus injection, the binding potential was calculated by the following methods. One approach is the kinetic analysis using the standard three-compartment model. Another is to define a transient equilibrium at the moment when the specific binding reaches its maximum. In continuous infusion, binding potential was calculated by using time-activity data at equilibrium condition. All methods gave almost identical binding potential, representing cross-validation of these methods. The continuous infusion method can provide "true" equilibrium condition. The kinetic analysis is a sophisticated approach but requires determination of an arterial input function. The transient equilibrium method thus is suitable for routine clinical research, since it does not require determination of an arterial input function.
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Affiliation(s)
- H Ito
- Karolinska Institutet, Department of Clinical Neuroscience, Karolinska Hospital, Stockholm, Sweden
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11
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Affiliation(s)
- S J Gatley
- Medical Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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12
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Koeppe RA, Frey KA, Kume A, Albin R, Kilbourn MR, Kuhl DE. Equilibrium versus compartmental analysis for assessment of the vesicular monoamine transporter using (+)-alpha-[11C]dihydrotetrabenazine (DTBZ) and positron emission tomography. J Cereb Blood Flow Metab 1997; 17:919-31. [PMID: 9307605 DOI: 10.1097/00004647-199709000-00001] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
This work compares equilibrium to kinetic analysis of positron emission tomography data for the assessment of vesicular monoamine transporter (VMAT2) binding density using (+)-alpha-[11C]dihydrotetrabenazine ((+)-alpha-[11C]DTBZ). Studies were performed for 80 minutes after intravenous administration of 18 +/- 1 mCi (+)-alpha-[11C]DTBZ on 9 young control subjects, 20 to 45 years of age. A 9-mCi bolus was injected over the first minute of the study, whereas the remaining 9 mCi were infused at a constant rate over the following 79 minutes. Steady-state was reached in both blood and brain by approximately 30 minutes after initiation of the study. Nonlinear least-squares analysis using two- and three-compartment models, weighted integral analysis using a two-compartment configuration, and Logan plot analysis all yielded kinetic estimates of the total tissue distribution volume, DVtot(kin). These results were compared with equilibrium distribution volume estimates, DVtot(eq), calculated from the tissue to metabolite corrected arterial plasma concentration ratio after 30 minutes. Kinetic modeling results from this study were in close agreement with prior bolus-injection (+)-alpha-[11C]DTBZ studies. In the current study, coefficients of variation in DVtot(kin) (19% to 23% across regions) and DVtot(eq) (18% to 22%) were nearly identical. Equilibrium estimates of DVtot were slightly lower than kinetic estimates, averaging 5% +/- 9% lower (P = 0.04, paired t test) in regions of high binding density (caudate and putamen), but only 2% +/- 6% (P = 0.09) in lower binding density regions (cortex, thalamus, cerebellum). DVtot(eq) estimates, however, still correlated highly with DVtot(kin) estimates (r = 0.977-0.989). Steady-state conditions can be achieved in both tissue and blood by 30 minutes, and the tissue-to-blood ratios of (+)-alpha-[11C]DTBZ at equilibrium yield DVtot(eq) measures that are in close agreement with DVtot(kin) estimates. Thus, a simple, easily tolerated protocol using a loading bolus followed by continuous infusion can provide excellent measures of VMAT2 binding.
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Affiliation(s)
- R A Koeppe
- Department of Internal Medicine, University of Michigan, Ann Arbor, USA
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Kilbourn M, Sherman P. In vivo binding of (+)-alpha-[3H]dihydrotetrabenazine to the vesicular monoamine transporter of rat brain: bolus vs. equilibrium studies. Eur J Pharmacol 1997; 331:161-8. [PMID: 9274975 DOI: 10.1016/s0014-2999(97)01054-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The regional rat brain distribution of (+)-alpha-[3H]dihydrotetrabenazine was determined following (a) infusion to equilibrium between brain and blood or (b) bolus injection. Infusions provide for direct measurement of total distribution volumes. The free plus nonspecific distribution volume for the brain was determined using infusion of very low specific activity (+)-alpha-[3H]dihydrotetrabenazine; specific distribution volumes, which represent specific radioligand binding, were then calculated as total minus the free + nonspecific distribution volume. Both total and specific distribution volumes correlated very well (r2 > 0.99) with in vitro distributions of the vesicular monoamine transporter binding site. Bolus injection, and measurement of radioactivity at a single time point, also provided regional estimates of radioligand binding which correlated well (r2 > 0.98) with in vitro values. The bolus method shows a small positive bias (+ 10-15%) in regions of high binding site concentrations. Both infusion and bolus injection methods give acceptable in vivo measures of (+)-alpha-[3H]dihydrotetrabenazine binding to the vesicular monoamine transporter of rat brain.
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Affiliation(s)
- M Kilbourn
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor 48109, USA.
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Cohen RM, Andreason PJ, Doudet DJ, Carson RE, Sunderland T. Opiate receptor avidity and cerebral blood flow in Alzheimer's disease. J Neurol Sci 1997; 148:171-80. [PMID: 9129113 DOI: 10.1016/s0022-510x(96)05315-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Positron emission tomography was performed on 12 Alzheimer's patients and 12 age-matched normal controls following the administration of the opiate receptor antagonist 6-deoxy-6-beta-[18F]fluoronaltrexone (cyclofoxy, CF). Tracer kinetic analysis was used to determine the volume of distribution of CF, a measure of unoccupied mu and kappa receptor density, i.e. opiate receptor avidity in 34 brain regions. Regional cerebral blood flow rates (CBF) were determined on the same day with H2[15O]. Global gray CF avidity and global gray CBF were found to be lower in the Alzheimer's patients and correlated (r=0.73, P<0.03). Regional CBF differences were superimposed on global CBF changes in the Alzheimer's patients, with the subcortex relatively spared. Multivariate statistical analyses, however, failed to demonstrate regional specificity for the CF avidity changes. Furthermore, percent changes in regional CF avidity were not correlated with percent changes in regional CBF (r=0.12, P=NS). These findings demonstrate involvement of the opiate system in Alzheimer's disease. Although, neurodegeneration is the likely underlying process responsible for both the changes in CF avidity and CBF in Alzheimer's disease, the differences with respect to the patterns of these losses suggest that the intermediate mechanisms leading from neurodegeneration to loss are distinct.
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Affiliation(s)
- R M Cohen
- Laboratory of Cerebral Metabolism, National Institute of Mental Health, Bethesda, MD 20892-4030, USA.
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Boulay SF, McRee RC, Cohen VI, Sood VK, Zeeberg BR, Reba RC. Specific binding component of the "inactive" stereoisomer (S,S)-[125I] IQNB to rat brain muscarinic receptors in vivo. Nucl Med Biol 1996; 23:211-9. [PMID: 8782228 DOI: 10.1016/0969-8051(95)02047-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In vivo nonspecific binding can be estimated using the inactive stereoisomer of a receptor radioligand. However, the binding of the inactive stereoisomer may be partially specific. Specific binding of the inactive (S,S)-[125I]IQNB was estimated from the inhibition induced by a competing nonradioactive ligand. This technique differed from the usual approach, since it was used to study the inactive rather than the active stereoisomer. The results indicate that there is substantial specific binding for (S,S)-[125I]IQNB.
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Affiliation(s)
- S F Boulay
- Department of Radiology, George Washington University Medical Center, Washington DC 20037, USA
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Videbaek C, Andersen JV, Dalgaard L, Foged C, Paulson OB, Lassen AN. Neuroreceptor quantification in vivo by the steady state principle and [123I]iomazenil in rats. Eur J Pharmacol 1995; 281:117-22. [PMID: 7589198 DOI: 10.1016/0014-2999(95)00205-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
A steady state method for neuroreceptor quantification in vivo in small laboratory animals is described, using [123I]iomazenil as tracer for the benzodiazepine receptor. The method was used for determination of the receptor equilibrium constant for a non-radioactive ligand, flumazenil, in rats and involved measurement of the nonspecific binding of [123I]iomazenil. Thirty-five animals were intravenously infused for 2 h with [123I]iomazenil and flumazenil in different proportions to obtain occupancies of the benzodiazepine receptor from close to 0 to about 99%. The nonspecific binding of iomazenil in brain tissue was calculated by an iterative procedure from the data for the highly blocked animals, and it was found to be 1.04 ml per ml plasma (n = 6). The mean cortical Kd of flumazenil was 21 +/- 11 nM (n = 19). The method is discussed with special reference to the problems of ascertaining steady state and nonspecific binding.
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Affiliation(s)
- C Videbaek
- Department of Neurology, National University Hospital, Rigshospitalet, Copenhagen, Denmark
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Yu DC, Huang SC, Barrio JR, Phelps ME. The assessment of the non-equilibrium effect in the 'Patlak analysis' of Fdopa PET studies. Phys Med Biol 1995; 40:1243-54. [PMID: 7568380 DOI: 10.1088/0031-9155/40/7/007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
'Patlak analysis' is a common approach used in Fdopa PET studies to calculate the uptake constant (Ki) of the tracer. It is assumed in the Patlak analysis that the reversible compartment of tissue radioactivity used is in effective equilibrium with the tracer in plasma. Therefore, using the data prior to equilibrium is in conflict with the assumption, and its effect on the estimate thus needs to be examined. In this study, we used simulations to investigate the errors due to the violation of the equilibrium assumption. Two factors affecting the estimate of Ki were examined--the eigenvalue of the model response function and the shape of the input function. The Ki estimate obtained from the Patlak analysis was found to be markedly biased because the system is not in equilibrium during the first 2 h post Fdopa injection. The magnitude of the bias was found to be dependent on the time interval used in the analysis (10% difference when comparing results from intervals 30-120 min and 60-120 min) and on the eigenvalue of the response function (10% change in Ki when the eigenvalue was changed by 20% around the nominal value). The estimates are also affected by the intersubject variations in the plasma time-activity curves. Therefore, Patlak analysis users should interpret their results with caution, particularly when examining small intersubject differences and small changes due to physiological or pharmacological interventions.
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Affiliation(s)
- D C Yu
- Department of Molecular and Medical Pharmacology, University of California, Los Angeles, USA
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Rinne JO, Burn DJ, Mathias CJ, Quinn NP, Marsden CD, Brooks DJ. Positron emission tomography studies on the dopaminergic system and striatal opioid binding in the olivopontocerebellar atrophy variant of multiple system atrophy. Ann Neurol 1995; 37:568-73. [PMID: 7755350 DOI: 10.1002/ana.410370505] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Ten patients with sporadic olivopontocerebellar atrophy and autonomic failure were studied with positron emission tomography. Subjects underwent both an [11C]diprenorphine and an [18F]fluorodopa scan. The mean caudate-occipital uptake ratio for [11C]diprenorphine was significantly reduced to 88% and the putamen-occipital uptake ratio to 85% of the control values. Individually, 4 of the 10 patients had significantly reduced opioid binding in the putamen. Mean putamen [18F]fluorodopa uptake was significantly diminished (to 71% of the control mean); individually 7 patients had significantly reduced uptake. There was a significant positive correlation between putamen-occipital uptake ratios for [11C]diprenorphine and putamen uptake of [18F]fluorodopa. Our results suggest that subclinical nigrostriatal dysfunction is present in the majority of patients with sporadic olivopontocerebellar atrophy, in accordance with it being part of the spectrum of multiple system atrophy.
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Affiliation(s)
- J O Rinne
- Medical Research Council Cyclotron Unit, Hammersmith Hospital, London, England
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19
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Moresco RM, Casati R, Lucignani G, Carpinelli A, Schmidt K, Todde S, Colombo F, Fazio F. Systemic and cerebral kinetics of 16 alpha [18F]fluoro-17 beta-estradiol: a ligand for the in vivo assessment of estrogen receptor binding parameters. J Cereb Blood Flow Metab 1995; 15:301-11. [PMID: 7860663 DOI: 10.1038/jcbfm.1995.35] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Estrogen receptors are expressed in several brain areas of various animal species, and steroid hormones exert physiologic and biochemical effects on the central nervous system. The aim of the present study was to evaluate in female adult rats, the suitability of 16 alpha [18F]fluoro-17 beta-estradiol ([18F]FES), a selective estrogen receptor ligand, for the in vivo assessment of brain estrogen receptors. This was considered to be a preliminary step in evaluating the potential usefulness of [18F]FES for studies of cerebral estrogen receptors with positron emission tomography (PET) in nonhuman primates and human subjects. We evaluated (a) the time course of the metabolic degradation of [18F]FES in blood; (b) the time course of distribution of the tracer in discrete cerebral areas; (c) the inhibitory effect of increasing doses of cold estradiol on cerebral [18F]FES uptake; and (d) the possibility of in vivo quantification of estrogen receptor binding parameters using both equilibrium and dynamic kinetic analyses. We quantified [18F]FES binding to estrogen receptors using both equilibrium and dynamic kinetic analyses. The results of this study indicate that [18F]FES is a suitable tracer for the measurement of estrogen receptors in the pituitary and hypothalamus, using either the equilibrium or the kinetic analysis. However, [18F]FES is inadequate for the in vivo investigation of estrogen binding sites in brain areas with low receptor density, such as the hippocampus.
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Affiliation(s)
- R M Moresco
- Department of Nuclear Medicine, University of Milan, Institute H. San Raffaele, Italy
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20
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Okocha CI, Kapczinski F, Lassen N, Lader MH. Central benzodiazepine receptor imaging and quantitation with single photon emission computerised tomography: SPECT. J Psychopharmacol 1995; 9:369-80. [PMID: 22298403 DOI: 10.1177/026988119500900412] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
This review discusses the current use of single photon emission computerised tomography (SPECT) for central benzodiazepine receptor imaging and quantitation. The general principles underlying SPECT imaging and receptor quantitation methods such as the kinetic, pseudo-equilibrium and steady-state (tracer infusion and bolus) approaches are described. The advantages and practical drawbacks of these techniques are highlighted.
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Affiliation(s)
- C I Okocha
- Clinical Psychopharmacology Section (MRC), Institute of Psychiatry, De Crespigny Park Denmark Hill, London SE5 8AF, UK
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21
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Malizia AL, Richardson MP. Benzodiazepine receptors and positron emission tomography: ten years of experience. A new beginning? J Psychopharmacol 1995; 9:355-68. [PMID: 22298402 DOI: 10.1177/026988119500900411] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Affiliation(s)
- A L Malizia
- Neuroscience Section, MRC Cyclotron Unit, Hammersmith Hospital, Du Cane Rd, London W12 0HS, Psychopharmacology Unit, University of Bristol, Bristol BS8 1TD, UK
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22
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Laruelle M, al-Tikriti MS, Zea-Ponce Y, Zoghbi SS, Baldwin RM, Charney DS, Hoffer PB, Kung HF, Innis RB. In vivo quantification of dopamine D2 receptor parameters in nonhuman primates with [123I]iodobenzofuran and single photon emission computerized tomography. Eur J Pharmacol 1994; 263:39-51. [PMID: 7821360 DOI: 10.1016/0014-2999(94)90521-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
[123I]Iodobenzofuran ([123I]IBF) is a new single photon emission computed tomography (SPECT) tracer for visualization of the dopamine D2 receptors. A tracer constant infusion paradigm was developed to measure the binding potential, density (Bmax) and affinity (KD) of the dopamine D2 receptor in baboons. Three baboons underwent both a single bolus and a constant infusion study. For the single bolus experiment, the striatal binding potential (134 +/- 24 ml g-1, mean +/- S.D.) was derived by kinetic analysis. For the constant infusion experiments, the striatal binding potential (127 +/- 16 ml g-1) was derived by equilibrium analysis. The two sets of experiments thus provided consistent data. Low specific activity constant infusion experiments were performed to measure KD (0.08 nM) and Bmax (12.7 nM). In vitro experiments carried out at 37 degrees C with [125I]IBF on rat striatal homogenate membranes provided results in agreement with the SPECT data. These studies suggested the feasibility of quantitation of dopamine D2 receptor parameters with [123I]IBF SPECT imaging.
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Affiliation(s)
- M Laruelle
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT
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23
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Gandelman MS, Baldwin RM, Zoghbi SS, Zea-Ponce Y, Innis RB. Evaluation of ultrafiltration for the free-fraction determination of single photon emission computed tomography (SPECT) radiotracers: beta-CIT, IBF, and iomazenil. J Pharm Sci 1994; 83:1014-9. [PMID: 7965658 DOI: 10.1002/jps.2600830718] [Citation(s) in RCA: 155] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
An ultrafiltration system was evaluated for the free-fraction measurement of SPECT radiotracers (beta-CIT, IBF, and iomazenil) used in functional brain imaging. The effect of temperature, storage, centrifugal force, tracer concentration, and percentage filtered demonstrated a relative error of < 9%. As a result of the minimal temperature effect, 25 degrees C was employed for all measurements. A comparison of the ultrafiltration system with equilibrium dialysis revealed < 5% difference for beta-CIT and iomazenil, but 16% for IBF. Additionally, the time and ease of operation considerably favored the ultrafiltration system. The precision quantitated by repetition was < 6% for between-run and within-run variability. In conclusion, ultrafiltration provided rapid results, demonstrated minor analytical errors, revealed generally good correlation with equilibrium dialysis, and allowed excellent precision.
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Affiliation(s)
- M S Gandelman
- Department of Psychiatry, Yale University School of Medicine, CT
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24
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Laruelle M, Abi-Dargham A, al-Tikriti MS, Baldwin RM, Zea-Ponce Y, Zoghbi SS, Charney DS, Hoffer PB, Innis RB. SPECT quantification of [123I]iomazenil binding to benzodiazepine receptors in nonhuman primates: II. Equilibrium analysis of constant infusion experiments and correlation with in vitro parameters. J Cereb Blood Flow Metab 1994; 14:453-65. [PMID: 8163587 DOI: 10.1038/jcbfm.1994.56] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In vivo benzodiazepine receptor equilibrium dissociation constant, KD, and maximum number of binding sites, Bmax, were measured by single photon emission computerized tomography (SPECT) in three baboons. Animals were injected with a bolus followed by a constant i.v. infusion of the high affinity benzodiazepine ligand [123I]iomazenil. Plasma steady-state concentration and receptor-ligand equilibrium were reached within 2 and 3 h, respectively, and were sustained for the duration (4-9 h) of the experiments (n = 15). At the end of the experiments, a receptor saturating dose of flumazenil (0.2 mg/kg) was injected to measure nondisplaceable activity. Experiments were carried out at various levels of specific activity, and Scatchard analysis was performed for derivation of the KD (0.59 +/- 0.09 nM) and Bmax (from 126 nM in the occipital region to 68 nM in the striatum). Two animals were killed and [125I]iomazenil Bmax and KD were measured at 22 and 37 degrees C on occipital homogenate membranes. In vitro values of Bmax (114 +/- 33 nM) and 37 degrees C KD (0.66 +/- 0.16 nM) were in good agreement with in vivo values measured by SPECT. This study demonstrates that SPECT can be used to quantify central neuroreceptors density and affinity.
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Affiliation(s)
- M Laruelle
- Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06516
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25
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Jones AK, Cunningham VJ, Ha-Kawa SK, Fujiwara T, Liyii Q, Luthra SK, Ashburner J, Osman S, Jones T. Quantitation of [11C]diprenorphine cerebral kinetics in man acquired by PET using presaturation, pulse-chase and tracer-only protocols. J Neurosci Methods 1994; 51:123-34. [PMID: 8051944 DOI: 10.1016/0165-0270(94)90002-7] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The quantitation of regional cerebral in vivo opioid receptor rate constants using [11C]diprenorphine and positron emission tomography (PET) using 3 types of protocol (presaturation, pulse-chase naloxone displacement and tracer-only protocols) together with measurements of regional cerebral blood flow is described in normal volunteers. Arterial blood was sampled continuously for radioactivity and was corrected for metabolites and plasma/blood partition of radioactivity to provide a continuous plasma input function. A compartmental model involving 3 tissue compartments was used to describe the regional cerebral pharmacokinetics of the tracer. The compartments comprised: (1) free plus rapidly exchanging non-specifically bound ligand, (2) specifically bound, naloxone displaceable ligand, and (3) a kinetically distinguishable non-specifically bound pool. Regional estimates of fractional rate constants relating to specific binding were obtained using naloxone in a pulse-chase design of tracer displacement. Less precise estimates of these rate constraints were obtained from single-tracer-only studies, but when binding was expressed as the tissue total volume of distribution relative to plasma there was good correlation with regional values obtained from pulse-chase studies performed in the same individuals. The application of these protocols to the measurement of indices of regional-specific opioid receptor binding in the human brain is discussed.
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Affiliation(s)
- A K Jones
- MRC Cyclotron Unit, Hammersmith Hospital, London, UK
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26
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al-Tikriti MS, Baldwin RM, Zea-Ponce Y, Sybirska E, Zoghbi SS, Laruelle M, Malison RT, Kung HF, Kessler RM, Charney DS. Comparison of three high affinity SPECT radiotracers for the dopamine D2 receptor. Nucl Med Biol 1994; 21:179-88. [PMID: 9234281 DOI: 10.1016/0969-8051(94)90007-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The regional brain distribution and pharmacological specificity of three high affinity tracers for the dopamine (DA) D2 receptor: [123I]IBF, [123I]epidepride, and [123I]2'-ISP were assessed by SPECT imaging of non-human primates. The ratios of striatal-to-occipital activities at the time of peak striatal uptake were 2.2, 6.3 and 1.7, respectively. From the peak striatal activities, washout rates were 33, 4 and 16%/h for [123I]IBF, [123I]epidepride and [123I]2'-ISP, respectively. The reversibility of the striatal uptake of all three agents was demonstrated by the rapid displacement induced by the dopamine D2 selective antipsychotic agent raclopride, which increased washout rates to 96, 58 and 43%/h. The administration of d-amphetamine, which induces release of dopamine, had no noticeable effect on [123I]epidepride but increased the washout rate of [123I]IBF. These results suggest that, among these three agents, [123I]epidepride is the superior tracer for in vivo displacement studies because of its slow washout and high target-to-background ratios. However, for tracer kinetic modeling, [123I]IBF may be the superior agent because of its early time of peak uptake and its higher target-to-background ratios than [123I]2'-ISP.
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Affiliation(s)
- M S al-Tikriti
- Department of Psychiatry, Yale University/VA Medical Center, West Haven, CT 06516, USA
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27
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Price JC, Mayberg HS, Dannals RF, Wilson AA, Ravert HT, Sadzot B, Rattner Z, Kimball A, Feldman MA, Frost JJ. Measurement of benzodiazepine receptor number and affinity in humans using tracer kinetic modeling, positron emission tomography, and [11C]flumazenil. J Cereb Blood Flow Metab 1993; 13:656-67. [PMID: 8391018 DOI: 10.1038/jcbfm.1993.84] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Kinetic methods were used to obtain regional estimates of benzodiazepine receptor concentration (Bmax) and equilibrium dissociation constant (Kd) from high and low specific activity (SA) [11C]flumazenil ([11C] Ro 15-1788) positron emission tomography studies of five normal volunteers. The high and low SA data were simultaneously fit to linear and nonlinear three-compartment models, respectively. An additional inhibition study (pretreatment with 0.15 mg/kg of flumazenil) was performed on one of the volunteers, which resulted in an average gray matter K1/k2 estimate of 0.68 +/- 0.08 ml/ml (linear three-compartment model, nine brain regions). The free fraction of flumazenil in plasma (f1) was determined for each study (high SA f1: 0.50 +/- 0.03; low SA f1: 0.48 +/- 0.05). The free fraction in brain (f2) was calculated using the inhibition K1/k2 ratio and each volunteer's mean f1 value (f2 across volunteers = 0.72 +/- 0.03 ml/ml). Three methods (Methods I-III) were examined. Method I determined five kinetic parameters simultaneously [K1, k2, k3 (= konf2Bmax), k4, and konf2/SA] with no priori constraints. An average kon value of 0.030 +/- 0.003 nM-1 min-1 was estimated for receptor-rich regions using Method I. In Methods II and III, the konf2/SA parameter was specifically constrained using the Method I value of kon and the volunteer's values of f2 and low SA (Ci/mumol). Four parameters were determined simultaneously using Method II. In Method III, K1/k2 was fixed to the inhibition value and only three parameters were estimated. Method I provided the most variable results and convergence problems for regions with low receptor binding. Method II provided results that were less variable but very similar to the Method I results, without convergence problems. However, the K1/k2 ratios obtained by Method II ranged from 1.07 in the occipital cortex to 0.61 in the thalamus. Fixing the K1/k2 ratio in Method III provided a method that was physiologically consistent with the fixed value of f2 and resulted in parameters with considerably lower variability. The average Bmax values obtained using Method III were 100 +/- 25 nM in the occipital cortex, 64 +/- 18 nM in the cerebellum, and 38 +/- 5.5 nM in the thalamus; the average Kd was 8.9 +/- 1.0 nM (five brain regions).
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Affiliation(s)
- J C Price
- Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, Maryland
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28
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Laruelle M, Abi-Dargham A, Rattner Z, al-Tikriti MS, Zea-Ponce Y, Zoghbi SS, Charney DS, Price J, Frost JJ, Hoffer PB. Single photon emission tomography measurement of benzodiazepine receptor number and affinity in primate brain: a constant infusion paradigm with [123I]iomazenil. Eur J Pharmacol 1993; 230:119-23. [PMID: 8381354 DOI: 10.1016/0014-2999(93)90421-d] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Benzodiazepine receptor number and affinity were measured in vivo with single photon emission tomography (SPECT). Following an initial bolus injection, the radiotracer [123I]iomazenil was infused at a constant rate for 5 to 8 h. This procedure induced a state of sustained equilibrium at the receptor level. Nondisplaceable activity was measured after injection of a receptor saturating dose of flumazenil. Experiments performed at high and low specific activity permitted estimation of an equilibrium binding affinity constant of 0.47 nM and a maximum binding capacity of 127 nM in occipital cortex.
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Affiliation(s)
- M Laruelle
- Department of Psychiatry, Yale University School of Medicine, New Haven, CT
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29
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Carson RE, Channing MA, Blasberg RG, Dunn BB, Cohen RM, Rice KC, Herscovitch P. Comparison of bolus and infusion methods for receptor quantitation: application to [18F]cyclofoxy and positron emission tomography. J Cereb Blood Flow Metab 1993; 13:24-42. [PMID: 8380178 DOI: 10.1038/jcbfm.1993.6] [Citation(s) in RCA: 310] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Positron emission tomography studies with the opiate antagonist [18F]cyclofoxy ([18F]CF) were performed in baboons. Bolus injection studies demonstrated initial uptake dependent on blood flow. The late uptake showed highest binding in caudate nuclei, amygdala, thalamus, and brainstem and the least accumulation in cerebellum. By 60 min postinjection, regional brain radioactivity cleared at the same rate as metabolite-corrected plasma, i.e., transient equilibrium was achieved. Compartmental modeling methods were applied to time-activity curves from brain and metabolite-corrected plasma. Individual rate constants were estimated with poor precision. The model estimate of the total volume of distribution (VT), representing the ratio of tissue radioactivity to metabolite-corrected plasma at equilibrium, was reliably determined. The apparent volume of distribution (Va), the concentration ratio of tissue to metabolite-corrected plasma during transient equilibrium, was compared with the fitted VT values to determine if single-scan methods could provide accurate receptor measurements. Va significantly overestimated VT and produced artificially high image contrast. These differences were predicted by compartment model theory and were caused by a plasma clearance rate that was close to the slowest tissue clearance rate. To develop a simple method to measure VT, an infusion protocol consisting of bolus plus continuous infusion (B/I) of CF was designed and applied in a separate set of studies. The Va values from the B/I studies agreed with the VT values from both B/I and bolus studies. This infusion approach can produce accurate receptor measurements and has the potential to shorten scan time and simplify the acquisition and processing of scan and blood data.
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Affiliation(s)
- R E Carson
- Positron Emission Tomography Department, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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30
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Lassen NA. Neuroreceptor quantitation in vivo by the steady-state principle using constant infusion or bolus injection of radioactive tracers. J Cereb Blood Flow Metab 1992; 12:709-16. [PMID: 1506439 DOI: 10.1038/jcbfm.1992.101] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The approaches hitherto used for measuring the kinetic constants Kd and Bmax of neuroreceptors in vivo all violate the steady state of the system. This complicates the kinetic analysis as approximations must be made, introducing errors of unknown magnitude. The present study presents the theory for designing experiments in which the steady state is preserved. It is based on maintaining a constant degree of receptor binding (occupancy) throughout the experiment. This is achieved by administering by prolonged intravenous infusion the non-radioactive ligand one wishes to study. The fraction of receptors sites not occupied by the "cold" ligand is measured by using trace amounts of a radioactive ligand binding to the same receptor. A minimum of two studies at different occupanies must be performed. In this presentation it is proposed to make the second study at essentially zero receptor occupancy by administering the tracer alone. The pair of tracer studies, the one without and the other with infusion of cold ligand, allows calculation of the cold ligand's equilibrium dissociation constant Kd. In the special case when tracer and cold ligands are chemically identical, then Bmax can also be calculated. Two different modes of tracer administration can be used. If the tracer is also infused at a constant rate for a long time, then the occupancy of receptor sites by the cold ligand can be calculated by measuring the equilibrium tracer concentrations in brain and plasma. If the tracer is administered as an intravenous bolus injection, then the area under the brain and plasma radioactivity curves or compartmental analysis must be used.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- N A Lassen
- Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, Copenhagen, Denmark
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