In acute ischemic stroke, understanding the dynamics of blood–brain barrier injury is of particular importance for the prevention of symptomatic hemorrhagic transformation. However, the available techniques assessing blood–brain barrier permeability are not quantitative and are little used in the context of acute reperfusion therapy. Nanoparticles cross the healthy or impaired blood–brain barrier through combined passive and active processes. Imaging and quantifying their transfer rate could better characterize blood–brain barrier damage and refine the delivery of neuroprotective agents. We previously developed an original endovascular stroke model of acute ischemic stroke treated by mechanical thrombectomy followed by positron emission tomography-magnetic resonance imaging. Cerebral capillary permeability was quantified for two molecule sizes: small clinical gadolinium Gd-DOTA (< 1 nm), and AGuIX® nanoparticles (∼5 nm) used for brain theranostics. On dynamic contrast-enhanced MRI, the baseline transfer constant Ktrans was 0.94 [0.48, 1.72] and 0.16 [0.08, 0.33] x10−3 min−1, respectively, in normal brain parenchyma, consistent with their respective sizes, and 1.90 [1.23, 3.95] and 2.86 [1.39, 4.52] x10−3 min−1 in choroid plexus, confirming higher permeability than brain parenchyma. At early reperfusion, Ktrans for both Gd-DOTA and AGuIX® nanoparticles was significantly higher within the ischemic area compared to the contralateral hemisphere; 2.23 [1.17, 4.13] and 0.82 [0.46, 1.87] x10−3 min−1 for Gd-DOTA and AGuIX® nanoparticles, respectively. With AGuIX® nanoparticles, Ktrans also increased within the ischemic growth areas, suggesting added value for AGuIX®. Finally, Ktrans was significantly lower in both the lesion and the choroid plexus in a drug-treated group (ciclosporin A, n = 7) compared to placebo (n = 5). Ktrans quantification with AGuIX® nanoparticles can monitor early blood–brain barrier damage and treatment effect in ischemic stroke after reperfusion.
Labeling of heterocycles with carbon‐11 is generally performed through peripheral functionalizations and more scarcely inside heterocyclic core. Such less common approach usually requires preliminary multi‐step synthesis of reactive species. Herein, a cyclization reaction by direct use of cyclotron‐produced [11C]CO2 is described to obtain various heterocycles intracyclically labeled in only 10 minutes.
Purpose F13640 (a.k.a. befiradol, NLX-112) is a highly selective 5-HT1A receptor ligand that was selected as a PET radiopharmaceutical-candidate based on animal studies. Due to its high efficacy agonist properties, [18F]F13640 binds preferentially to functional 5-HT1A receptors, which are coupled to intracellular G-proteins. Here, we characterize brain labeling of 5-HT1A receptors by [18F]F13640 in humans and describe a simplified model for its quantification. Methods PET/CT and PET-MRI scans were conducted in a total of 13 healthy male volunteers (29 ± 9 years old), with arterial input functions (AIF) (n = 9) and test–retest protocol (n = 8). Several kinetic models were compared (one tissue compartment model, two-tissue compartment model, and Logan); two models with reference region were also evaluated: simplified reference tissue model (SRTM) and the logan reference model (LREF). Results [18F]F13640 showed high uptake values in raphe nuclei and cortical regions. SRTM and LREF models showed a very high correlation with kinetic models using AIF. As concerns test–retest parameters and the prolonged binding kinetics of [18F]F13640, better reproducibility, and reliability were found with the LREF method. Cerebellum white matter and frontal lobe white matter stand out as suitable reference regions. Conclusion The favorable brain labeling and kinetic profile of [18F]F13640, its high receptor specificity and its high efficacy agonist properties open new perspectives for studying functionally active 5-HT1A receptors, unlike previous radiopharmaceuticals that act as antagonists. [18F]F13640’s kinetic properties allow injection outside of the PET scanner with delayed acquisitions, facilitating the design of innovative longitudinal protocols in neurology and psychiatry. Trial Registration. Trial Registration EudraCT 2017–002,722-21.
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