Measurement of Protein Synthesis Rate in Rat by [11C]Leucine PET Imaging: Application to the TgF344-AD Model of Alzheimer's Disease.

Long-term memory requires stable protein synthesis and is altered in Alzheimer's disease (AD). This study aimed to implement a method to measure the cerebral protein synthesis rate (PSR) with [11C]leucine PET in vivo in rats and evaluate potential PSR alterations longitudinally (6, 12 and 18 months old) in the TgF344-AD rat model of AD. Wistar, wild-type (WT) and TgF344-AD rats (TG) were scanned for 60 min with [11C]leucine. Arterial blood activity was monitored online and with discrete whole blood and plasma samples by γ-counting in Wistar rats, WT (n = 4) and TG (n = 5). Unlabelled amino acids were measured in plasma. The sensitivity of [11C]leucine PET to measure alterations in PSR was assessed in Wistar rats by injection of PSR inhibitor anisomycin before PET acquisition. Anisomycin administration significantly reduced the net uptake rate constant (Kcplx) of [11C]leucine and PSR, proving the suitability of the method. For the longitudinal study, averaged population-based input functions were used to calculate PSR. We found a significant genotype effect on PSR (decrease in TG vs WT) only in the globus pallidus. This study suggests that [11C]leucine PET is sensitive enough to measure brain PSR in rat but that cross-sectional design with individual input function should be preferred.

Development of a method for the preparation of zirconium-89 radiolabelled chitosan nanoparticles as an application for leukocyte trafficking with positron emission tomography.

Positron Emission Tomography is an attractive imaging modality for monitoring the migration of cells to pathological tissue. We evaluated a new method for radiolabelling leukocytes with zirconium-89 (89Zr) using chitosan nanoparticles (CN, Z-average size 343 ± 210nm and zeta potential +46 ± 4mV) as the carrier. We propose that cell uptake of 89Zr-loaded CN occurred in a two-step process; cell membrane interaction with 89Zr-loaded CN was followed by a slower cell internalisation step.

Early changes in extracellular matrix in Alzheimer's disease.

AIMS: Although changes in extracellular matrix (ECM) scaffold have been reported previously in Alzheimer's disease (AD) compared to normal ageing, it is not known how alterations in the numerous components of the perivascular ECM might occur at different stages of AD. This study therefore investigates potential changes in basement membrane-associated ECM molecules in relation to increasing Braak stages. METHODS: Thirty patients were divided into three groups (control subject, subclinical AD and AD patients). ECM levels of collagen IV, perlecan and fibronectin as well as human platelet endothelial cell adhesion molecule (hPECAM) were quantified by immunohistochemistry. Von Willebrand factor staining was measured to assess vessel density. Expression levels were correlated with the presence of amyloid plaques. RESULTS: Collagen IV, perlecan and fibronectin expression was increased in subclinical AD and AD patients when compared to controls, in frontal and temporal cortex, whilst no further increase was detected between subclinical AD and AD. These changes were not associated with an increase in vessel density, which was instead decreased in the temporal cortex of AD patients. In contrast, hPECAM levels remained unchanged. Finally, we found similar pattern in levels of amyloid deposition between the different Braak stages and showed that changes in ECM components correlated with amyloid deposition. CONCLUSION: Present data support the hypothesis that significant ECM changes occur during the early stages of AD. ECM changes affecting brain microvascular functions could therefore drive disease progression and provide potential new early investigational biomarkers in AD.

A new technique for the radiolabelling of mixed leukocytes with zirconium-89 for inflammation imaging with positron emission tomography.

Mixed leukocyte (white blood cells [WBCs]) trafficking using positron emission tomography (PET) is receiving growing interest to diagnose and monitor inflammatory conditions. PET, a high sensitivity molecular imaging technique, allows precise quantification of the signal produced from radiolabelled moieties. We have evaluated a new method for radiolabelling WBCs with either zirconium-89 ((89) Zr) or copper-64 ((64) Cu) for PET imaging. Chitosan nanoparticles (CNs) were produced by a process of ionotropic gelation and used to deliver radiometals into WBCs. Experiments were carried out using mixed WBCs freshly isolated from whole human blood. WBCs radiolabelling efficiency was higher with [(89) Zr]-loaded CN (76.8 ± 9.6% (n = 12)) than with [(64) Cu]-loaded CN (26.3 ± 7.0 % (n = 7)). [(89) Zr]-WBCs showed an initial loss of 28.4 ± 5.8% (n = 2) of the radioactivity after 2 h. This loss was then followed by a plateau as (89) Zr remains stable in the cells. [(64) Cu]-WBCs showed a loss of 85 ± 6% (n = 3) of the radioactivity after 1 h, which increased to 96 ± 6% (n = 3) loss after 3 h. WBC labelling with [(89) Zr]-loaded CN showed a fast kinetic of leukocyte association, high labelling efficiency and a relatively good retention of the radioactivity. This method using (89) Zr has a potential application for PET imaging of inflammation.

Contribution of interleukin-1 receptor accessory protein B to interleukin-1 actions in neuronal cells.

Interleukin (IL)-1 is an important neuroimmunomodulator and a key mediator of inflammation during brain disorders. It acts on neuronal and glial cells via binding to the IL-1 type 1 receptor and IL-1 receptor accessory protein (IL-1RAcP). More recently, a neuronal-specific isoform of IL-1RAcP, named IL-1RAcPb, has been identified. Our aim was to determine the role of IL-1RAcPb in IL-1 actions in neuronal and glial cells, and to further explore the signaling mechanisms of IL-1 in neurons. We found that IL-1RAcPb deletion had no effect on IL-1α- and IL-1ß-induced activation of the extracellular signal-regulated kinase 1/2 or IL-6 release in glial cultures, although IL-6 release in response to high IL-1α concentration (30 IU/ml) was significantly reduced. We identified the p38 kinase as a key signaling element in IL-1α- and IL-1ß-induced IL-6 synthesis and release in neuronal cultures. IL-1RAcPb deletion had no effect on IL-1α- and IL-1ß-induced IL-6 release in neurons, but significantly reduced IL-1α- but not IL-1ß-induced p38 phosphorylation. Our data demonstrate that the p38 signaling pathway plays an important role in IL-1 actions in neurons, and that IL-1RAcP may regulate some, but not all, neuronal activities in response to IL-1α.

Biodistribution, pharmacokinetics and metabolism of interleukin-1 receptor antagonist (IL-1RA) using [¹8F]-IL1RA and PET imaging in rats.

BACKGROUND AND PURPOSE: Positron emission tomography (PET) has the potential to improve our understanding of the preclinical pharmacokinetics and metabolism of therapeutic agents, and is easily translated to clinical studies in humans. However, studies involving proteins radiolabelled with clinically relevant PET isotopes are currently limited. Here we illustrate the potential of PET imaging in a preclinical study of the biodistribution and metabolism of ¹8F-labelled IL-1 receptor antagonist ([¹8F]IL-1RA) using a novel [¹8F]-radiolabelling technique. EXPERIMENTAL APPROACH: IL-1RA was radiolabelled by reductive amination on lysine moieties with [¹8F]fluoroacetaldehyde. Sprague-Dawley rats were injected intravenously with [¹8F]IL-1RA and imaged with a PET camera for 2 h. For the study of IL-1RA metabolites by ex vivoγ-counting of samples, rats were killed 20 min, 1 h or 2 h after injection of [¹8F]IL-1RA. KEY RESULTS: [¹8F]IL-1RA distribution into the major organs of interest was as follows: kidneys >> liver > lungs >> brain. In lungs and liver, [¹8F]IL-1RA uptake peaked within 1 min post-injection then decreased rapidly to reach a plateau from 10 min post-injection. In the brain, the uptake exhibited slower pharmacokinetics with a smaller post-injection peak and a plateau from 6 min onward. IL-1RA was rapidly metabolized and these metabolites represented ∼40% of total activity in plasma and ∼80% in urine, 20 min after injection. CONCLUSIONS AND IMPLICATIONS Preclinical PET imaging is a feasible method of assessing the biodistribution of new biological compounds of therapeutic interest rapidly. The biodistribution of [¹8F]IL-1RA reported here is in agreement with an earlier study suggesting low uptake in the normal brain, with rapid metabolism and excretion via the kidneys.

Radiolabeling with fluorine-18 of a protein, interleukin-1 receptor antagonist.

IL-1RA is a naturally occurring antagonist of the pro-inflammatory cytokine interleukin-1 (IL-1) with high therapeutic promise, but its pharmacokinetic remains poorly documented. In this report, we describe the radiolabeling of recombinant human interleukin-1 receptor antagonist (rhIL-1RA) with fluorine-18 to allow pharmacokinetic studies by positron emission tomography (PET). rhIL-1RA was labeled randomly by reductive alkylation of free amino groups (the epsilon-amino group of lysine residues or amino-terminal residues) using [(18)F]fluoroacetaldehyde under mild reaction conditions. Radiosyntheses used a remotely controlled experimental rig within 100min and the radiochemical yield was in the range 7.1-24.2% (decay corrected, based on seventeen syntheses). We showed that the produced [(18)F]fluoroethyl-rhIL-1ra retained binding specificity by conducting an assay on rat brain sections, allowing its pharmakokinetic study using PET.

Asthma counselling targeted to removal of domestic animals.

OBJECTIVES: To create and evaluate the efficacy of a short individualized educational intervention program, based on Prochaska's transtheoretical model, for a six-month period in a population of adult asthma patients living with domestic animals but sensitized to these pets. METHODS: A randomized, controlled study using a pretested questionnaire was conducted at three different times (pretest, and at three and six months postintervention). RESULTS: Eleven members (29%) of the intervention group and eight members (21%) of the control group removed their pets within six months (X(2)=3.23; P>0.35). The two groups showed similar improvements in their perception of the benefits of pet removal and in their level of belief that they could do it. The experimental group showed a greater improvement in knowledge acquisition about asthma and allergies than the control group (P<0.05). Both experimental and standard educational interventions were effective in facilitating progression through the stages of behavioural change. CONCLUSION: Overall, the results do not support the utility of behavioural change educational intervention, tailored to the transtheoretical model stage of the individual, in the context of convincing patients to remove their pets from their homes. However, the decision-making aid appears to be helpful in raising awareness of the problem of asthma and allergy in the patient, and in developing appropriate knowledge.

Improved synthesis of the peripheral benzodiazepine receptor ligand [11C]DPA-713 using [11C]methyl triflate.

Recently, the pyrazolopyrimidine, [11C] N,N-Diethyl-2-[2-(4-methoxyphenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl]acetamide (DPA-713) has been reported as a new promising marker for the study of peripheral benzodiazepine receptors with positron emission tomography. In the present study, DPA-713 has been labelled from the corresponding nor-analogue using [11C]methyl triflate (CH3OTf). Conditions for HPLC were also modified to include physiological saline (aq. 0.9% NaCl)/ethanol:60/40 as mobile phase making it suitable for injection. The total time of radiosynthesis, including HPLC purification, was 18-20 min. This reported synthesis of [11C]DPA-713, using [11C]CH3OTf, resulted in an improved radiochemical yield (30-38%) compared to [11C]methyl iodide (CH3I) (9) with a simpler purification method. This ultimately enhances the potential of [11C]DPA-713 for further pharmacological and clinical evaluation. These improvements make this radioligand more suitable for automated synthesis which is of benefit where multi-dose preparations and repeated syntheses of radioligand are required.

Interleukin-1 in the brain: mechanisms of action in acute neurodegeneration.

Interleukin-1 (IL-1) exerts a number of diverse actions in the brain, and it is currently well accepted that it contributes to experimentally induced neurodegeneration. Much of this is based on studies using the IL-1 receptor antagonist, which inhibits cell death caused by ischemia, brain injury, or excitotoxins. Our aim is to determine how and where in the brain IL-1 acts to produce these effects. Most of the neurodegenerative effects of IL-1 are thought to be through IL-1 beta. However, we have data implicating IL-1 alpha in excitotoxic cell death. Furthermore mice lacking both IL-1 alpha and IL-1 beta show dramatically reduced ischemic cell death, whereas deletion of IL-1 alpha or IL-1 beta alone fails to modify damage. It has also been demonstrated that IL-1 exacerbates ischemic injury in mice in the absence of the type I IL-1 receptor, suggesting the existence of novel IL-1 receptors in the brain. IL-1 also dramatically exacerbates neuronal loss in response to intrastriatal administration of the excitotoxin AMPA in the rat brain, an effect accompanied by marked increases in cytokine expression in the frontoparietal cortex, which precedes subsequent cell death in this region. Intrastriatal AMPA also results in limbic seizures that are exacerbated by IL-1, and we hypothesize, therefore, that IL-1 exacerbates cell death through increased seizure activity. Therefore, IL-1 appears to induce acute neurodegeneration through a number of mechanisms.

Role of IL-1alpha and IL-1beta in ischemic brain damage.

The cytokine interleukin-1 (IL-1) has been strongly implicated in the pathogenesis of ischemic brain damage. Evidence to date suggests that the major form of IL-1 contributing to ischemic injury is IL-1beta rather than IL-1alpha, but this has not been tested directly. The objective of the present study was to compare the effects of transient cerebral ischemia [30 min middle cerebral artery occlusion (MCAO)] on neuronal injury in wild-type (WT) mice and in IL-1alpha, IL-1beta, or both IL-1alpha and IL-1beta knock-out (KO) mice. Mice lacking both forms of IL-1 exhibited dramatically reduced ischemic infarct volumes compared with wild type (total volume, 70%; cortex, 87% reduction). Ischemic damage compared with WT mice was not significantly altered in mice lacking either IL-1alpha or IL-1beta alone. IL-1beta mRNA, but not IL-1alpha or the IL-1 type 1 receptor, was strongly induced by MCAO in WT and IL-1alpha KO mice. Administration (intracerebroventricularly) of recombinant IL-1 receptor antagonist significantly reduced infarct volume in WT (-32%) and IL-1alpha KO (-48%) mice, but had no effect on injury in IL-1beta or IL-1alpha/beta KO mice. These data confirm that IL-1 plays a major role in ischemic brain injury. They also show that chronic deletion of IL-1alpha or IL-1beta fails to influence brain damage, probably because of compensatory changes in the IL-1 system in IL-1alpha KO mice and changes in IL-1-independent mediators of neuronal death in IL-1beta KO mice.

Influence of asthma education on asthma severity, quality of life and environmental control.

BACKGROUND: Several studies have examined the influence of asthma education, focusing mainly on the use of health services. OBJECTIVES: To assess the influence of an asthma education program (AEP) on airway responsiveness, asthma symptoms, patient quality of life (QOL) and environmental control. DESIGN: A prospective, randomized, controlled study with parallel groups. SETTING: Three tertiary care hospitals in Quebec. POPULATION: One hundred and eighty-eight patients with moderate to severe asthma. INTERVENTION: After optimization of asthma treatment with inhaled corticosteroids, patients were randomly assigned to receive either an education program based on self-management (group E) or usual care (control group C). RESULTS: One year after an AEP, there was a significant decrease in the number of days per month without daytime asthma symptoms in group E only (P=0.03). Asthma daily symptom scores decreased significantly in group E in comparison with group C (P=0. 006). QOL scores improved markedly in both groups after treatment optimization during the run-in period (P<0.01). After an AEP, the QOL score increased further in group E patients in comparison with group C patients (P=0.04). The concentration of methacholine that induces a 20% fall in forced expiratory volume in 1 s (PC20) improved significantly in both groups (group E 1.2+/-1.1 to 2.4+/-0. 2, group C 1.5+/-1.2 to 2.4+/-1.3, P<0.01). After one year, 26 of 37 patients from group E sensitized to house dust mites (HDM) adopted the specific measures recommended to reduce their exposure to HDM, while none of the 21 subjects from group C did (P<0.001). Among the patients sensitized to cats or dogs, 15% of patients from group E and 23% of patients in group C no longer had a pet at home at the final visit (P>0.5). CONCLUSIONS: One year after the educational intervention, it was observed that the program had added value over and above that of optimization of medication and regular clinical follow-ups. The education program was highly effective in promoting HDM avoidance measures but minimally effective for removing domestic animals, suggesting that more efficient strategies need to be developed for the latter.

Influence of corticotrophin releasing factor on neuronal cell death in vitro and in vivo.

Several studies have demonstrated that antagonists of the corticotrophin releasing factor (CRF) receptor markedly inhibit experimentally induced excitotoxic, ischaemic and traumatic brain injury in the rat, and that CRF expression is elevated in response to experimentally induced stroke or traumatic brain injury. CRF is also induced by the pro-inflammatory cytokine interleukin 1 (IL-1), which participates in various forms of neurodegeneration. The aim of this study was to test the hypothesis that CRF is toxic directly in vivo or in vitro. In primary cultures of rat cortical neurons, exposure to CRF (10 pM-100 nM) for 24 h failed to cause cell death directly, or to modify the neurotoxic effects of N-methyl-D-aspartate (NMDA). Similarly, infusion of CRF (0.3-5 microg) into specific brain regions of the rat did not induce cell death and did not significantly alter the neuronal damage produced by infusion of excitatory amino acids. These data demonstrate that CRF is not directly neurotoxic, and suggest that either CRF mediates neuronal damage by indirect actions (e.g. on the vasculature) and/or that CRF is not the endogenous ligand which contributes to neurodegeneration through activation of CRF receptors.

Exofocal alterations in opioidergic receptor densities following focal cerebral ischemia in the mouse.

In previous studies of our group, we have reported differential alterations in opioidergic receptor subtypes densities in infarcted and periinfarcted brain tissue following middle cerebral artery occlusion (MCAO) in mice. Other studies have also described subcortical alterations consecutive to focal cortical ischemia. For a better understanding of ischemic processes in exofocal areas, we have investigated the evolution of opioidergic receptors following focal cortical ischemia through the quantification of relative binding densities, B(max) and K(d) values for the mu, delta, and kappa subtypes. Our results demonstrate that opioid receptor subtypes exhibit adaptations at distance from the ischemic core, mainly in the striatum, the thalamus, and the substantia nigra. Indeed, mu and delta B(max) values were increased in ventral thalamic nuclei, while kappa relative binding densities were transiently increased in nucleus medialis dorsalis and nucleus lateralis, pars posterior. Moreover, the B(max) of mu and delta receptors were transiently decreased at 6 h post-MCAO in ipsi- and contralateral patches and matrices of the striatum. Conversely, the mu B(max) values were increased in ipsi- and contralateral substantia nigra, pars compacta, and pars reticulata, 24 h following MCAO. In contralateral substantia nigra, pars compacta, kappa B(max) was found to be decreased at 24 h post-MCAO. These alterations could reflect neuronal dysfunction in exofocal brain structures, consecutively to the degeneration of defined neuroanatomical pathways. Our study indicates that opioidergic receptors could be used as markers of the neuronal reorganization that take place in subcortical areas following an ischemic insult of the brain cortex.

Differential time-course decreases in nonselective, mu-, delta-, and kappa-opioid receptors after focal cerebral ischemia in mice.

BACKGROUND AND PURPOSE: Neuroprotection studies have demonstrated the involvement of opioids in ischemia, and we have previously demonstrated alterations in Bmax of opioidergic receptors after 2 post-MCAO time points in mice. METHODS: In the present study, we have investigated in a detailed manner the postischemic time course of variations in [3H]diprenorphine (nonselective), [3H]DAMGO (mu), [3H]DADLE (delta), and [3H]U69593 (kappa) relative binding densities after focal cerebral ischemia (0 to 48 hours) in mice. RESULTS: In frontoparietal cortices, our results demonstrate decreases in (1) delta receptor densities at 1 to 3 hours after MCAO, (2) mu and nonselective binding sites at 6 to 12 hours after MCAO, and (3) kappa receptor densities between 6 and 24 hours after MCAO. In the rostral part of the infarct border zone, a decrease in delta-receptors was found concomitant with the extension of the infarct core; conversely, the decrease in delta-receptors appeared before (6 to 12 hours) macroscopic histological damage, which occurred between 12 hours and 24 hours after MCAO in the caudal part of this area. In this frontier, mu- and especially kappa-binding sites were decreased later (12 to 48 hours after MCAO). CONCLUSIONS: These differential alterations in opioidergic receptors could be due to the selective sublocalization of receptors, postsynaptically on cortical interneurons for mu- and delta-receptors versus presynaptically on cortical afferent pathways for the kappa subtype. Further, our results suggest that delta- and mu-opioidergic receptors could be markers of infarct extension and neuronal death; the study of [3H]diprenorphine and selective binding sites argues in favor of the use of receptor-specific ligands. Finally, the relative preservation of kappa-receptors might be correlated with the neuroprotective role of kappa-agonists, as previously reported.

Potential mechanisms of interleukin-1 involvement in cerebral ischaemia.

Interleukin-1 (IL-1) has pleiotropic actions in the central nervous system. During the last decade, a growing corpus of evidence has indicated an important role of this cytokine in the development of brain damage following cerebral ischaemia. The expression of IL-1 in the brain is dramatically increased during the early and chronic stage of infarction. The most direct evidence that IL-1 contributes significantly to ischaemic injury is that (1) central administration of IL-1beta exacerbates brain damage, and (2) injection or over-expression of interleukin-1 receptor antagonist, and blockade of interleukin-1beta converting enzyme activity reduce, dramatically, infarction and improve behavioural deficit. The mechanisms underlying IL-1 actions in stroke are not definitively elucidated, and it seems likely that its effects are mediated through stimulation and inhibition of wide range of pathophysiological processes.

Maximal densities of mu, delta, and kappa receptors are differentially altered by focal cerebral ischaemia in the mouse.

Though opioids are known to have neuroprotective properties, little information is available on the functional state of opioidergic receptors following focal cerebral ischaemia. The present study investigated the evolution of the Bmax and Kd for [3H]DAMGO, [3H]DADLE, and [3H]U69,593, respectively, for the mu, delta, and kappa opioidergic receptors after permanent focal cerebral ischaemia in mice. While the various Kd were unchanged, mu and delta Bmax values were precociously decreased in frontoparietal cortices, earlier than kappa receptors, reflecting infarct extension with time. The Bmax values for mu and delta receptors were also altered in non-infarcted tissues, such as tissues at risk (e.g., temporal auditory cortex) and exofocal (e.g., contralateral and non-infarcted) cortices. These results suggest that, in non-infarcted areas, the observed changes reflect functional modifications to focal ischaemia.

Influence on asthma morbidity of asthma education programs based on self-management plans following treatment optimization.

The objective of this study was to evaluate the effectiveness of an asthma education program on morbidity, knowledge, and compliance with inhaled corticosteroid treatment using a prospective, randomized, controlled, one-year-before/one-year-after protocol. After rigorous optimization of asthma therapy under the care of respirologists, patients were assigned to one of three groups: Group C (control group: no formal education), Group P (education and action plan based on peak-flow monitoring), and Group S (education with action plan based on monitoring of asthma symptoms). A total of 188 subjects with moderate to severe asthma were enrolled and 149 completed the study. Asthma morbidity decreased significantly in all groups (p = 0.001). Mean values one-year-before/one-year-after in Groups C, P, and S were: unscheduled medical visits, 2.4/0.8, 2.3/0.7, and 1.9/ 0.7; hospitalizations, 0.21/0.04, 0.24/0.04, and 0.40/0.09; oral steroid treatments; 1.3/0.5, 1.2/0.7, and 1.3/0.9; absenteeism from work/school, 9.6/5.2, 8.8/2.2, and 6.3/2.9. Between-group differences did not reach statistical significance (p > 0.05). Asthma knowledge increased in both educated groups compared with the control group (p < 0.001) as did short-term compliance with inhaled corticosteroids. These results confirm that treatment optimization coupled with sustained high quality care in motivated patients can lead to a significant decrease in asthma morbidity. In such clinical settings, structured asthma education significantly improved short-term compliance with treatment and knowledge about asthma, although it could not add extra benefit with regard to morbidity. Nevertheless, this study does not refute the potential benefit of educational interventions aimed at improving asthma-related morbidity over a longer time period or in patients with less optimal care or with high-risk factors.

Apoptotic death in cortical neurons of mice subjected to focal ischemia.

Permanent focal cortical ischemia was induced in mice by electrocoagulation of the middle cerebral artery. At different time intervals after the injury, the volume of infarction was assessed together with an analysis of neuronal death. Morphological studies of ischemic brains and detection of nucleosomal DNA ladder within ipsilateral cortices might implicate a component of this neuronal loss to apoptosis as well as necrosis. Furthermore, we used the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling) procedure to detect in situ DNA fragmentation. The localization and the proportion of apoptotic cells in the ischemic mouse brain would indicate that apoptosis contributes largely to the cellular loss induced by cerebral ischemia.

In vivo binding, pharmacokinetics and metabolism of the selective M2 muscarinic antagonists [3H]AF-DX 116 and [3H]AF-DX 384 in the anesthetized rat.

The pharmacokinetics, in vivo binding and metabolism of two M2 muscarinic receptor antagonists, [3H]AF-DX 116 and [3H]AF-DX 384, were studied in anesthetized rats, which received either the tracer alone or following a saturating injection of atropine. Both radioligands were cleared from the circulation with distribution half-lives of 17 and 14 sec and elimination half-lives of 17 and 40 min for [3H]AF-DX 116 and [3H]AF-DX 384, respectively. A radioactive distribution, predominant in peripheral organs when compared to brain, was found at each time studied after tracer injection. Atropine-displaceable tracer uptake was evidenced at 20-40 min in brain (31%), submandibular glands (26%), spleen (37%) and notably heart (55%) for [3H]AF-DX 116 but only in heart (50%) for [3H]AF-DX 384 at 10-20 min. Regional brain sampling revealed a relatively uniform distribution of [3H]AF-DX 384 and a -45% atropine saturation effect (i.e., specific binding) in the thalamus 20 min after injection. Sequential thin-layer chromatographic studies performed on tissue extracts demonstrated the rapid appearance of labeled metabolites of both radiotracers in brain (but less so in liver) and especially in cardiac tissues, where almost 70% of total radioactivity still corresponded to authentic tracer 40 min after injection. Thus, based on their low blood-brain barrier permeability and the high presence of labeled metabolites in the central nervous system, AF-DX 116 and AF-DX 384 might be more helpful in the study of M2 muscarinic receptors present in heart rather than brain. Labeled with positron emittors, these M2 antagonists might be applicable to the pathophysiological study of disease states, such as cardiomyopathies.