scholarly journals Quantitation of Extrastriatal D2 Receptors Using a Very High-Affinity Ligand (FLB 457) and the Multi-Injection Approach

1999 ◽  
Vol 19 (5) ◽  
pp. 533-546 ◽  
Author(s):  
Jacques Delforge ◽  
Michel Bottlaender ◽  
Christian Loc'h ◽  
Ilonka Guenther ◽  
Chantal Fuseau ◽  
...  
Keyword(s):  
D2 Receptor ◽  
Free Ligand ◽  
Brain Regions ◽  
Model Parameters ◽  
Tracer Injection ◽  
High Affinity ◽  
Precise Knowledge ◽  
Receptor Sites ◽  
Very High

The multi-injection approach has been used to study in baboon the in vivo interactions between the D2 receptor sites and FLB 457, a ligand with a very high affinity for these receptors. The model structure was composed of four compartments (plasma, free ligand, and specifically and unspecifically bound ligands) and seven parameters (including the D2 receptor site density). The arterial plasma concentration, after correction for metabolites, was used as the input function, The experimental protocol, which consisted of three injections of labeled and/or unlabeled ligand, allowed the evaluation of all model parameters from a single positron emission tomography experiment In particular, the concentration of receptor sites available for binding ( B'max) and the apparent in vivo FLB 457 affinity were estimated in seven brain regions, including the cerebellum and several cortex regions, in which these parameters are estimated in vivo for the first time ( B'max is estimated to be 4,0 ± 1.3 pmol/mL in the thalamus and from 0.32 to 1.90 pmol/mL in the cortex), A low receptor density was found in the cerebellum ( B'max = 0.39 ± 0.17 pmol/mL), whereas the cerebellum is usually used as a reference region assumed to be devoid of D2 receptor sites, In spite of this very small concentration (1 % of the striatal concentration), and because of the high affinity of the ligand, we demonstrated that after a tracer injection, most of the PET-measured radioactivity in the cerebellum results from the labeled ligand bound to receptor sites, The estimation of all the model parameters allowed simulations that led to a precise knowledge of the FLB 457 kinetics in all brain regions and gave the possibility of testing the equilibrium hypotheses and estimating the biases introduced by the usual simplified approaches.

Effects of Heparin Oligosaccharides with High Affinity for Antithrombin III in Experimental Venous Thrombosis

1982 ◽  
Vol 47 (03) ◽  
pp. 244-248 ◽  
Author(s):  
D P Thomas ◽  
Rosemary E Merton ◽  
T W Barrowcliffe ◽  
L Thunberg ◽  
U Lindahl
Keyword(s):  
Antithrombin Iii ◽  
Specific Activity ◽  
High Specific Activity ◽  
Factor Xa ◽  
Blood Levels ◽  
Thrombin Time ◽  
High Affinity ◽  
Very High

SummaryThe in vitro and in vivo characteristics of two oligosaccharide heparin fragments have been compared to those of unfractionated mucosal heparin. A decasaccharide fragment had essentially no activity by APTT or calcium thrombin time assays in vitro, but possessed very high specific activity by anti-Factor Xa assays. When injected into rabbits at doses of up to 80 ¼g/kg, this fragment was relatively ineffective in impairing stasis thrombosis despite producing high blood levels by anti-Xa assays. A 16-18 monosaccharide fragment had even higher specific activity (almost 2000 iu/mg) by chromogenic substrate anti-Xa assay, with minimal activity by APTT. When injected in vivo, this fragment gave low blood levels by APTT, very high anti-Xa levels, and was more effective in preventing thrombosis than the decasaccharide fragment. However, in comparison with unfractionated heparin, the 16-18 monosaccharide fragment was only partially effective in preventing thrombosis, despite producing much higher blood levels by anti-Xa assays.It is concluded that the high-affinity binding of a heparin fragment to antithrombin III does not by itself impair venous thrombogenesis, and that the anti-Factor Xa activity of heparin is only a partial expression of its therapeutic potential.

scholarly journals Parametric Images of the Extrastriatal D2 Receptor Density Obtained Using a High-Affinity Ligand (FLB 457) and a Double-Saturation Method

2001 ◽  
Vol 21 (12) ◽  
pp. 1493-1503 ◽  
Author(s):  
Jacques Delforge ◽  
Michel Bottlaender ◽  
Christian Loc'h ◽  
Frédéric Dolle ◽  
André Syrota
Keyword(s):  
Dopamine Receptors ◽  
Quantitative Estimation ◽  
Temporal Cortex ◽  
D2 Receptor ◽  
Experimental Protocol ◽  
D2 Dopamine Receptors ◽  
High Affinity ◽  
Receptor Sites ◽  
Receptor Concentration ◽  
Saturation Method

The potential of positron emission tomography for the quantitative estimation of receptor concentration in extrastriatal regions has been limited in the past because of the low density of the D2 receptor sites in these regions and the insufficient affinity of the most widely used radioligands for dopamine receptors. The new method described in this paper permits the estimate of the D2 receptor concentration in the extrastriatal regions using a two-injection protocol and FLB 457, a ligand with a high affinity (20 pmol/L in vitro) with D2 dopamine receptors. This approach is not valid for the striatal regions because some hypotheses cannot be verified (because of the high receptor concentration in these regions). The experimental protocol includes two injections with ligand doses designed to significantly occupy the extrastriatal receptor sites (≈ 90%), while leaving less than 60% of the receptor sites occupied by the ligand in the striatal regions. The results obtained using this double-saturation method are in line with the concentration estimates previously obtained using the multiinjection approach. The receptor concentration is 2.9 ± 0.5 pmol/mL in the thalamus, 1.0 ± 0.2 pmol/mL in the temporal cortex, and 0.35 ± 0.13 pmol/mL in the occipital cortex. This study provides new arguments supporting the presence of a small receptor-site concentration in the cerebellum, estimated at 0.35 ± 0.16 pmol/mL The simplicity of the calculation used to estimate the receptor concentration lends itself easily to parametric imaging. The receptor concentration is estimated pixel by pixel, without filtering. This method permits estimation of the extrastriatal D2 receptor concentration using an experimental protocol that can easily be used in patient studies (i.e., single experiment, no blood sampling, short experiment duration).

scholarly journals Erythropoietin receptors on murine erythroid colony-forming units: natural history

Blood ◽  
1989 ◽  
Vol 73 (6) ◽  
pp. 1476-1486 ◽  
Author(s):  
KT Landschulz ◽  
AN Noyes ◽  
O Rogers ◽  
SH Boyer
Keyword(s):  
Growth Function ◽  
Gene Products ◽  
Half Time ◽  
High Affinity ◽  
Receptor Sites ◽  
Colony Forming Units ◽  
Computer Aided ◽  
Dissociation Constant Kd ◽  
Zero Time

Abstract Erythropoietin (Epo) response and binding was assessed in purified murine CFU-E and their descendants. Several features emerged. First, Epo on CFU-E is in rapid flux: Half-time for 125I-Epo internalization is approximately four to five minutes. Second, computer-aided Scatchard analyses indicate that greater than 70 high-affinity Epo-receptor sites on anemic animal CFU-E are sometimes already occupied by Epo acquired in vivo. When this is removed, 40% of greater than or equal to 370 sites per CFU-E belong to a high-affinity class (dissociation constant, kd: 73 pmol/L +/- 15 [SE]) and 60% belong to a low-affinity class (kd: 813 pmol/L +/- 246). Third, the few small colonies that develop from CFU-E in the absence of Epo are shown, by serial assay of 59Fe-heme biosynthesis, to stem from contaminating erythroblasts: a result consistent with our finding that, after eight-hour CFU-E culture, most erythroblasts no longer require appreciable Epo for growth. Thus, although the early need for Epo by CFU-E is nearly absolute, this need is not met by the often substantial Epo already on board. The inference is that repeated occupancy of the rapidly turning over Epo receptors is required. Fourth, Epo bound and/or internalized by CFU-E descendants decreases to 40% of zero-time levels after 14 hours in Epo-supplemented culture and disappears after 28 hours. Scatchard analyses indicate that 73 pmol/L kd receptor sites become undetectable at seven to eight hours, whereas 813 pmol/L kd sites are undiminished and only one-third less by 16 hours. This apparent disappearance of high-affinity sites and persistence of low-affinity sites suggests that (a) at least two gene products mediate Epo binding, eg, two different receptor polypeptides or one receptor and one cofactor which modulates affinity; (b) high-affinity sites mediate the growth function of Epo during the first eight hours of culture; and (c) lingering low-affinity receptors may mediate some unrecognized Epo function. Fifth, the efficiency with which 106- and 91-Kd CFU-E membrane polypeptides can be cross-linked to 125I-Epo is two- to threefold higher for cells labeled at high Epo concentrations than at low ones, which suggests that these polypeptides largely reflect low-affinity site reactions.

scholarly journals Monoclonal Antibodies against Extracellular Domains of Claudin-1 Block Hepatitis C Virus Infection in a Mouse Model

2015 ◽  
Vol 89 (9) ◽  
pp. 4866-4879 ◽  
Author(s):  
Masayoshi Fukasawa ◽  
Shotaro Nagase ◽  
Yoshitaka Shirasago ◽  
Manami Iida ◽  
Mayo Yamashita ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Hcv Infection ◽  
Dependent Manner ◽  
Entry Inhibitors ◽  
High Affinity ◽  
Extracellular Domains ◽  
Very High

ABSTRACTHepatitis C virus (HCV) entry into host cells is a complex process requiring multiple host factors, including claudin-1 (CLDN1). Safe and effective therapeutic entry inhibitors need to be developed. We isolated a human hepatic Huh7.5.1-derived cell mutant that is nonpermissive to HCV, and comparative microarray analysis showed that the mutant was CLDN1 defective. Four hybridomas were obtained, which produced monoclonal antibodies (MAbs) that interacted with the parental Huh7.5.1 cell but not with the CLDN1-defective mutant. All MAbs produced by these hybridomas specifically bound to human CLDN1 with a very high affinity and prevented HCV infection of Huh7.5.1 cells in a dose-dependent manner, without apparent cytotoxicity. Two selected MAbs also inhibited HCV infection of human liver-chimeric mice without significant adverse effects. CLDN1 may be a potential target to prevent HCV infectionin vivo. Anti-CLDN1 MAbs may hence be promising candidates as novel anti-HCV agents.IMPORTANCESafe and effective therapeutic entry inhibitors against hepatitis C virus (HCV) are very useful for combination therapies with other anti-HCV drugs, such as direct-acting antivirals. In this study, we first showed an effective strategy for developing functional monoclonal antibodies (MAbs) against extracellular domains of a multimembrane-spanning target protein, claudin-1 (CLDN1), by using parental cells expressing the intact target membrane protein and target-defective cells. The established MAbs against CLDN1, which had a very high affinity for intact CLDN1, efficiently inhibitedin vitroandin vivoHCV infections. These anti-CLDN1 MAbs are promising leads for novel entry inhibitors against HCV.

Polymerization of Enbucrilate/Lipiodol Mixtures In Vivo

2000 ◽  
Author(s):  
Matthew J. Gounis ◽  
Baruch B. Lieber ◽  
L. Nelson Hopkins
Keyword(s):  
High Speed ◽  
Polymerization Kinetics ◽  
Polymerization Process ◽  
Embolic Agent ◽  
Model Parameters ◽  
Normal Brain ◽  
Normal Density ◽  
Precise Knowledge ◽  
Kinetics Of

Abstract Embolization is an endovascular procedure used to treat cerebral arteriovenous malformations (AVMs). AVMs are pathological shunts between arteries and veins, which bypass normal brain structures. An embolic agent commonly used to occlude AVMs is n-butyl 2-cyanoacrylate (NBCA). Although NBCA has shown to be efficacious for this application, precise knowledge of its polymerization process in vivo is needed. Inadvertent occlusion of arterial feeders proximal to the AVM nidus will occur when polymerization of NBCA is too rapid. This may lead to revascularization of the AVM. Conversely, long polymerization times may result in the occlusion of draining veins, with subsequent brain hemorrhage and pulmonary emboli. It is therefore critical to understand the kinetics of the polymerization process to obtain a complete glue cast of the arteriovenous transition (nidus) thus, yielding safe obliteration of the AVM. In order to elucidate the polymerization kinetics of NBCA, we examined the embolization process in the femoral and subclavian arteries of the rabbit. Various embolic agents composed of NBCA/lipiodol mixtures with and without the addition of glacial acetic acid (GAA) were injected. Blood flow through the femoral and subclavian arteries was measured prior to and during embolization. All studies were recorded with high-speed digital subtraction angiography (DSA). Preliminary analysis of the data suggests that flow decay during embolization exhibits a behavior that can be modeled via a lagged-normal density curve. Optimized model parameters vis a vis the experimental data are related to the polymerization kinetics. These parameters can be used to form a quantitative basis of comparison for the various liquid embolic mixtures.

Comparison of Two Compartmental Models for Describing Receptor Ligand Kinetics and Receptor Availability in Multiple Injection PET Studies

1996 ◽  
Vol 16 (5) ◽  
pp. 841-853 ◽  
Author(s):  
Evan D. Morris ◽  
Nathaniel M. Alpert ◽  
Alan J. Fischman
Keyword(s):  
Specific Activity ◽  
Tissue Response ◽  
High Rate ◽  
Receptor Modeling ◽  
Model Parameters ◽  
Multiple Injection ◽  
Positron Emission ◽  
Receptor Sites ◽  
Tracer Kinetic

The goal of research with receptor ligands and PET is the characterization of an in vivo system that measures rates of association and dissociation of a ligand-receptor complex and the density of available binding sites. It has been suggested that multiple injection studies of radioactive ligand are more likely to identify model parameters than are single injection studies. Typically, at least one of the late injections is at a low specific activity (SA), so that part of the positron emission tomography (PET) curve reflects ligand dissociation. Low SA injections and the attendant reductions in receptor availability, however, may violate tracer kinetic assumptions, namely, tracer may no longer be in steady state with the total (labeled and unlabeled) ligand. Tissue response becomes critically dependent on the dose of total ligand, and an accurate description of the cold ligand in the tissue is needed to properly model the system. Two alternative models have been applied to the receptor modeling problem, which reduces to describing the time-varying number of available receptor sites. The first ( Huang et al., 1989 ) contains only compartments for the hot ligand, ‘hot only’ (HO), but indirectly accounts for the action of cold ligand at receptor sites via SA. The second stipulates separate compartments for the hot and cold ligands, ‘hot and cold’ (HC), thus explicitly calculating available number of receptors. We examined these models and contrasted their abilities to predict PET activity, receptor availability, and SA in each tissue compartment. For multiple injection studies, the models consistently predicted different PET activities—especially following the third injection. Only for very high rate constants were the models identical for multiple injections. In one case, simulated PET curves were quite similar, but discrepancies appeared in predictions of receptor availability. The HO model predicted nonphysiological changes in the availability of receptor sites and introduced errors of 30–60% into estimates of B′max for test data. We, therefore, strongly recommend the use of the HC model for all analyses of multiple injection PET studies.

PET studies of D2-receptor binding in striatal and extrastriatal brain regions: Biochemical support in vivo for separate dopaminergic systems in humans

Synapse ◽  
2010 ◽  
Vol 64 (6) ◽  
pp. 478-485 ◽  
Author(s):  
Simon Cervenka ◽  
Andrea Varrone ◽  
Erik Fransén ◽  
Christer Halldin ◽  
Lars Farde
Keyword(s):  
Receptor Binding ◽  
D2 Receptor ◽  
Brain Regions ◽  
Dopaminergic Systems

High affinity dopamine D2 receptor radioligands. 3. [123I] and [125I]epidepride: In vivo studies in rhesus monkey brain and comparison with in vitro pharmacokinetics in rat brain

Life Sciences ◽  
1993 ◽  
Vol 53 (3) ◽  
pp. 241-250 ◽  
Author(s):  
Robert M. Kessler ◽  
John R. Votaw ◽  
Dennis E. Schmidt ◽  
M. Sib Ansari ◽  
Karen P. Holdeman ◽  
...  
Keyword(s):  
Rhesus Monkey ◽  
Rat Brain ◽  
Dopamine D2 Receptor ◽  
D2 Receptor ◽  
In Vivo Studies ◽  
Monkey Brain ◽  
High Affinity ◽  
Rhesus Monkey Brain

scholarly journals Dual-[11C]Tracer Single-Acquisition Positron Emission Tomography Studies

2001 ◽  
Vol 21 (12) ◽  
pp. 1480-1492 ◽  
Author(s):  
Robert A. Koeppe ◽  
David M. Raffel ◽  
Scott E. Snyder ◽  
Edward P. Ficaro ◽  
Michael R. Kilbourn ◽  
...  
Keyword(s):  
Positron Emission Tomography ◽  
Computer Simulations ◽  
Emission Tomography ◽  
Parameter Estimates ◽  
Model Parameters ◽  
Tracer Injection ◽  
Positron Emission ◽  
Dynamic Scan ◽  
Dual Tracer

The ability to study multiple physiologic processes of the brain simultaneously within the same subject would provide a new means to explore the interactions between neurotransmitter systems in vivo. Currently, examination of two distinct neuropharmacologic measures with positron emission tomography (PET) necessitates performing two separate scans spaced in time to allow for radionuclide decay. The authors present results from a dual-tracer PET study protocol using a single dynamic-scan acquisition where the injections of two tracers are offset by several minutes. Kinetic analysis is used to estimate neuropharmacologic parameters for both tracers simultaneously using a combined compartmental model configuration. This approach results in a large reduction in total study time of nearly 2 hours for carbon-11–labeled tracers. As multiple neuropharmacologic measures are obtained at nearly the same time, interventional protocols involving a pair of dual-tracer scans become feasible in a single PET session. Both computer simulations and actual human PET studies were performed using combinations of three different tracers: [11C]flumazenil, N-[11C]methylpiperidinyl propionate, and [11C]dihydrotetrabenazine. Computer simulations of tracer-injection separations of 10 to 30 minutes showed the feasibility of the approach for separations down to 15 to 20 minutes or less. Dual-tracer PET studies were performed in 32 healthy volunteers using injection separations of 10, 15, or 20 minutes. Model parameter estimates for each tracer were similar to those obtained from previously performed single-injection studies. Voxel-by-voxel parametric images were of good quality for injections spaced by 20 minutes and were nearly as good for 15-minute separations, but were degraded noticeably for some model parameters when injections were spaced by only 10 minutes. The authors conclude that dual-tracer single-scan PET is feasible, yields accurate estimates of multiple neuropharmacologic measures, and can be implemented with a number of different radiotracer pairs.

Sign in / Sign up

Export Citation Format

Share Document