[F-18]Atorvastatin Pharmacokinetics and Biodistribution in Healthy Female and Male Rats

Statins are 3-hydroxy-3-methylglutaryl- coenzyme A reductase inhibitors that are widely used to prevent cardiovascular diseases. However, a series of pleiotropic mechanisms have been associated with statins, particularly with atorvastatin. Therefore, the assessment of [F-18]atorvastatin kinetics with positron emission tomography (PET) may elucidate the mechanism of action of statins and the impact of sexual dimorphism, which is one of the most debated interindividual variations influencing the therapeutic efficacy. [F-18]Atorvastatin was synthesized via a previously optimized F-18-deoxyfluorination strategy, used for preclinical PET studies in female and male Wistar rats (n = 7 for both groups), and for subsequent ex vivo biodistribution assessment. PET data were fitted to several pharmacokinetic models, which allowed for estimating relevant kinetic parameters. Both PET imaging and biodistribution studies showed negligible uptake of [F-18]atorvastatin in all tissues compared with the primary target organ (liver), excretory pathways (kidneys and small intestine), and stomach. Uptake of [F-18]atorvastatin was 38 +/- 3% higher in the female liver than in the male liver. The irreversible 2-tissue compartment model showed the best fit to describe [F-18]atorvastatin kinetics in the liver. A strong correlation (R-2 &gt; 0.93) between quantitative Ki (the radiotracer's unidirectional net rate of influx between compartments) and semi-quantitative liver's SUV (standard uptake value), measured between 40 to 90 min, showed potential to use the latter parameter, which circumvents the need for blood sampling as a surrogate of Ki for monitoring [F-18]atorvastatin uptake. Preclinical assays showed faster uptake and clearance for female rats compared to males, seemingly related to a higher efficiency for exchanges between the arterial input and the hepatic tissue. Due to the slow [F-18]atorvastatin kinetics, equilibrium between the liver and plasma concentration was not reached during the time frame studied, making it difficult to obtain sufficient and accurate kinetic information to quantitatively characterize the radiotracer pharmacokinetics over time. Nevertheless, the reported results suggest that the SUV can potentially be used as a simplified measure, provided all scans are performed at the same time point. Preclinical PET-studies with [F-18]atorvastatin showed faster uptake and clearance in female compared to male rats, apparently related to higher efficiency for exchange between arterial blood and hepatic tissue.</p

Eltoprazine Suppresses Hyperpolarizing Responses to Serotonin in Rat Hippocampus

ABSTRACT In this study we report the effects of eltoprazine, a phenylpiperazine derivative with high affinity for 5-hydroxytryptamine

Perivascular adipose tissue-derived nitric oxide compensates endothelial dysfunction in aged pre-atherosclerotic apolipoprotein E-deficient rats

BACKGROUND AND AIMS: Atherosclerosis is a major contributor to global mortality and is accompanied by vascular inflammation and endothelial dysfunction. Perivascular adipose tissue (PVAT) is an established regulator of vascular function with emerging implications in atherosclerosis. We investigated the modulation of aortic relaxation by PVAT in aged rats with apolipoprotein E deficiency (ApoE-/-) fed a high-fat diet as a model of early atherosclerosis. METHODS AND RESULTS: ApoE-/- rats (N = 7) and wild-type Sprague-Dawley controls (ApoE+/+, N = 8) received high-fat diet for 51 weeks. Hyperlipidemia was confirmed in ApoE-/- rats by elevated plasma cholesterol (p < 0.001) and triglyceride (p = 0.025) levels. Early atherosclerosis was supported by increased intima/media thickness ratio (p < 0.01) and ED1-positive macrophage influx in ApoE-/- aortic intima (p < 0.001). Inflammation in ApoE-/- PVAT was characteristic by an increased [18F]FDG uptake (p < 0.01), ED1-positive macrophage influx (p = 0.0003), mRNA expression levels of CD68 (p < 0.001) and IL-1β (p < 0.01), and upregulated iNOS protein (p = 0.011). The mRNAs of MCP-1, IL-6 and adiponectin remained unchanged in PVAT. Aortic PVAT volume measured with micro-PET/CT was increased in ApoE-/- rats (p < 0.01). Maximal endothelium-dependent relaxation (EDR) to acetylcholine in ApoE-/- aortic rings without PVAT was severely impaired (p = 0.012) compared with controls, while ApoE-/- aortic rings with PVAT showed higher EDR than controls. All EDR responses were blocked by L-NMMA and the expression of eNOS mRNA was increased in ApoE-/- PVAT (p = 0.035). CONCLUSION: Using a rat ApoE-/- model of early atherosclerosis, we capture a novel mechanism by which inflammatory PVAT compensates severe endothelial dysfunction by contributing NO upon cholinergic stimulation

In vivo evaluation of [F-18]FEAnGA-Me:a PET tracer for imaging beta-glucuronidase (beta-GUS) activity in a tumor/inflammation rodent model

Introduction: The PET tracer, 1-O-(4-(2-fluoroethyl-carbamoyloxymethyl)-2-nitrophenyl)-O-beta-D-glucopyronuronate ([F-18]FEAnGA), was recently developed for PET imaging of extracellularl beta-glucuronidase (beta-GUS). However,[F-18]FEAnGA exhibited rapid renal clearance, which resulted in a relatively low tracer uptake in the tumor. To improve the pharmacokinetics of [F-18]FEAnGA, we developed its more lipophilic methyl ester analog, [F-18]FEAnGA-Me. Methods: [F-18]FEAnGA-Me was obtained by alkylation of the O-protected glucuronide methyl ester precursor with [F-18]-fluoroethylamine ([F-18]FEA), followed by removal of the acetate protecting groups with NaOMe/MeOH. The PET tracer was evaluated by in vitro and in vivo studies. Results: [F-18]FEAnGA-Me was obtained in 5%-10% overall radiochemical yield. It is 10-fold less hydrophilic than [F-18]FEAnGA and it is stable in PBS and in the presence of beta-GUS for 1 h. However, in the presence of esterase or plasma [F-18]FEAnGA-Me is converted to [F-18]FEAnGA, and subsequently converted to [F-18]FEA by beta-GUS. MicroPET studies in Wistar rats bearing a C6 glioma and a sterile inflammation showed similar uptake in tumors after injection of either [F-18]FEAnGA-Me or [F-18]FEAnGA. Both tracers had a rapid two-phase clearance of total plasma radioactivity with a half-life of 1 and 8 min. The [F-18]FEAnGA fraction generated from [F-18]FEAnGA-Me by in vivo hydrolysis had a circulation half-life of 1 and 11 min in plasma. Similar distribution volume in the viable part of the tumor was found after injection of either [F-18]FEAnGA-Me or [F-18]FEAnGA. Conclusion: The imaging properties of [F-18]FEAnGA-Me were not significantly better than those of [F-18]FEAnGA. Therefore, other strategies should be applied in order to improve the kinetics of these tracers. (C) 2012 Elsevier Inc. All rights reserved

Pridopidine selectively occupies sigma-1 rather than dopamine D2 receptors at behaviorally active doses

Dopamine stabilizers have stimulatory actions under low dopamine tone and inhibitory actions under high dopamine tone without eliciting catalepsy. These compounds are dopamine D-2 receptor (D2R) antagonists or weak partial agonists and may have pro-mnemonic and neuroprotective effects. The mechanism underlying their stimulatory and neuroprotective actions is unknown but could involve sigma-1R binding. The present study examined sigma-1R and D2R occupancy by the dopamine stabilizer pridopidine (ACR16) at behaviorally relevant doses in living rats. Rats were administered 3 or 15 mg/kg pridopidine, or saline, before injection of the radiotracer C-11-SA4503 (sigma-1R) or C-11-raclopride (D2R). Some animals received 60 mg/kg pridopidine and were only scanned with C-11-raclopride. Cerebral C-11-SA4503 binding was quantified using metabolite-corrected plasma input data and distribution volume (V (T)) calculated by Logan graphical analysis. C-11-raclopride binding was quantified using striatum-to-cerebellum ratios and binding potentials calculated with a simplified reference tissue model. Cunningham-Lassen plots indicated sigma-1R occupancies of 57 +/- 2 and 85 +/- 2 % after pretreatment of animals with 3 and 15 mg/kg pridopidine. A significant (44-66 %) reduction of C-11-raclopride binding was only observed at 60 mg/kg pridopidine. At doses shown to elicit neurochemical and behavioral effects, pridopidine occupied a large fraction of sigma-1Rs and a negligible fraction of D(2)Rs. Significant D2R occupancy was only observed at a dose 20-fold higher than was required for sigma-1R occupancy. The characteristics of dopamine stabilizers may result from the combination of high sigma-1R and low D2R affinity

Test-retest repeatability of [18F]MC225-PET in rodents:A tracer for imaging of P-gp function

In longitudinal PET studies, animals are repeatedly anesthetized which may affect the repeatability of PET measurements. The aim of this study was to assess the effect of anesthesia on the P-gp function as well as the reproducibility of [18F]MC225 PET scans. Thus, dynamic PET scans with blood sampling were conducted in 13 Wistar rats. Seven animals were exposed to isoflurane anesthesia 1 week before the PET scan ("Anesthesia-exposed" PET). A second group of six animals was used to evaluate the reproducibility of measurements of P-gp function at the blood-brain barrier (BBB) with [18F]MC225. In this group, two PET scans were made with a 1 week interval ("Test" and "Retest" PET). Pharmacokinetic parameters were calculated using compartmental models and metabolite-corrected plasma as an input function. "Anesthesia-exposed" animals showed a 28% decrease in whole-brain volume of distribution (VT) (p < 0.001) compared to "Test", where the animals were not previously anesthetized. The VT at "Retest" also decreased (19%) compared to "Test" (p < 0.001). The k2 values in whole-brain were significantly increased by 18% in "Anesthesia-exposed" (p = 0.005) and by 15% in "Retest" (p = 0.008) compared to "Test". However, no significant differences were found in the influx rate constant K1, which is considered as the best parameter to measure the P-gp function. Moreover, Western Blot analysis did not find significant differences in the P-gp expression of animals not pre-exposed to anesthesia ("Test") or pre-exposed animals ("Retest"). To conclude, anesthesia may affect the brain distribution of [18F]MC225 but it does not affect the P-gp expression or function

Mapping Arginase Expression with ¹⁸F-Fluorinated Late-Generation Arginase Inhibitors Derived from Quaternary α-Amino Acids

Arginase hydrolyzes L-arginine and influences levels of polyamines and nitric oxide. Arginase overexpression is associated with inflammation and tumorigenesis. Thus, radiolabeled arginase inhibitors may be suitable PET tracers for staging arginase-related pathophysiologies. We report the synthesis and evaluation of 2 radiolabeled arginase inhibitors, 18F-FMARS and 18F-FBMARS, developed from α-substituted-2-amino-6-boronohexanoic acid derivatives. Methods: Arylboronic ester-derived precursors were radiolabeled via copper-mediated fluorodeboronation. Binding assays using arginase-expressing PC3 and LNCaP cells were performed. Autoradiography of lung sections from a guinea pig model of asthma overexpressing arginase and dynamic small-animal PET imaging with PC3-xenografted mice evaluated the radiotracers' specific binding and pharmacokinetics. Results:18F-fluorinated compounds were obtained with radiochemical yields of up to 5% (decay-corrected) and an average molar activity of 53 GBq⋅μmol-1 Cell and lung section experiments indicated specific binding that was blocked up to 75% after pretreatment with arginase inhibitors. Small-animal PET studies indicated fast clearance of the radiotracers (7.3 ± 0.6 min), arginase-mediated uptake, and a selective tumor accumulation (SUV, 3.0 ± 0.7). Conclusion: The new 18F-fluorinated arginase inhibitors have the potential to map increased arginase expression related to inflammatory and tumorigenic processes. 18F-FBMARS showed the highest arginase-mediated uptake in PET imaging and a significant difference between uptake in control and arginase-inhibited PC3 xenografted mice. These results encourage further research to examine the suitability of 18F-FBMARS for selecting patients for treatments with arginase inhibitors

Pharmacokinetic Modeling of [11C]GSK-189254, PET Tracer Targeting H3 Receptors, in Rat Brain

[Image: see text] The histamine H(3) receptor has been considered as a target for the treatment of various central nervous system diseases. Positron emission tomography (PET) studies with the radiolabeled potent and selective histamine H(3) receptor antagonist [(11)C]GSK-189254 in rodents could be used to examine the mechanisms of action of novel therapeutic drugs or to assess changes of regional H(3) receptor density in animal models of neurodegenerative disease. [(11)C]GSK-189254 was intravenously administered to healthy Wistar rats (n = 10), and a 60 min dynamic PET scan was carried out. Arterial blood samples were obtained during the scan to generate a metabolite-corrected plasma input function. PET data were analyzed using a one-tissue compartment model (1T2k), irreversible (2T3k) or reversible two-tissue compartment models (2T4k), graphical analysis (Logan and Patlak), reference tissue models (SRTM and SRTM2), and standard uptake values (SUVs). The Akaike information criterion and the standard error of the estimated parameters were used to select the most optimal quantification method. This study demonstrated that the 2T4k model with a fixed blood volume fraction and Logan graphical analysis can best describe the kinetics of [(11)C]GSK-189254 in the rat brain. SUV(40–60) and the reference tissue-based measurements DVR(2T4k), BP(ND)(SRTM), and SUV ratio could also be used as a simplified method to estimate H(3) receptor availability in case blood sampling is not feasible

Binding of the Dual-Action Anti-Parkinsonian Drug AG-0029 to Dopamine D-2 and Histamine H-3 Receptors:A PET Study in Healthy Rats

Introduction: Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor dysfunction and a diverse range of nonmotor symptoms. Functional relationships between the dopaminergic and histaminergic systems suggest that dual-action pharmaceuticals like AG-0029 (D-2/D-3 agonist/H-3 antagonist) could ameliorate both the motor and cognitive symptoms of PD. The current study aimed to demonstrate the interaction of AG-0029 with its intended targets in the mammalian brain using positron emission tomography (PET). Methods: Healthy male Wistar rats were scanned with a small-animal PET camera, using either the dopamine D-2/D-3 receptor ligand [C-11]raclopride or the histamine H-3 receptor ligand [C-11]GSK-189254, before and after treatment with an intravenous, acute, single dose of AG-0029. Dynamic [C-11]raclopride PET data (60 min duration) were analyzed using the simplified reference tissue model 2 (SRTM2) with cerebellum as reference tissue and the nondisplaceable binding potential as the outcome parameter. Data from dynamic [C-11]GSK-189254 scans (60 min duration) with arterial blood sampling were analyzed using Logan graphical analysis with the volume of distribution (V-T) as the outcome parameter. Receptor occupancy was estimated using a Lassen plot. Results: Dopamine D-2/3 receptor occupancies in the striatum were 22.6 +/- 18.0 and 84.0 +/- 3.5% (mean +/- SD) after administration of 0.1 and 1 mg/kg AG-0029, respectively. In several brain regions, the V-T values of [C-11]GSK-189254 were significantly reduced after pretreatment of rats with 1 or 10 mg/kg AG-0029. The H-3 receptor occupancies were 11.9 +/- 8.5 and 40.3 +/- 11.3% for the 1 and 10 mg/kg doses of AG-0029, respectively. Conclusions: Target engagement of AG-0029 as an agonist at dopamine D-2/D-3 receptors and an antagonist at histamine H-3 receptors could be demonstrated in the rat brain with [C-11]raclopride and [C-11]GSK-189254 PET, respectively. The measured occupancy values reflect the previously reported high (subnanomolar) affinity of AG-0029 to D-2/D-3 and moderate (submicromolar) affinity to H-3 receptors

Multivalency in healable supramolecular polymers: the effect of supramolecular cross-link density on the mechanical properties and healing of non- covalent polymer networks

Polymers with the ability to heal themselves could provide access to materials with extended lifetimes in a wide range of applications such as surface coatings, automotive components and aerospace composites. Here we describe the synthesis and characterisation of two novel, stimuli-responsive, supramolecular polymer blends based on p-electron-rich pyrenyl residues and p-electron-deficient, chain-folding aromatic diimides that interact through complementary p–p stacking interactions. Different degrees of supramolecular “cross-linking” were achieved by use of divalent or trivalent poly(ethylene glycol)-based polymers featuring pyrenyl end-groups, blended with a known diimide–ether copolymer. The mechanical properties of the resulting polymer blends revealed that higher degrees of supramolecular “cross-link density” yield materials with enhanced mechanical properties, such as increased tensile modulus, modulus of toughness, elasticity and yield point. After a number of break/heal cycles, these materials were found to retain the characteristics of the pristine polymer blend, and this new approach thus offers a simple route to mechanically robust yet healable materials