Abstract
Epinephrine (E) and norepinephrine (NE) play diverse roles in our body’s physiology. In addition to their role in the peripheral nervous system (PNS), E/NE systems including their receptors are critical to the central nervous system (CNS) and to mental health. Various antipsychotics, antidepressants, and psychostimulants exert their influence partially through different subtypes of adrenergic receptors (ARs). Despite the potential of pharmacological applications and long history of research related to E/NE systems, research efforts to identify the roles of ARs in the human brain taking advantage of imaging have been limited by the lack of subtype specific ligands for ARs and brain penetrability issues. This review provides an overview of the development of positron emission tomography (PET) radiotracers for in vivo imaging of AR system in the brain.
Highlights
Positron emission tomography (PET) is a noninvasive and highly sensitive in vivo imaging technique that uses small amounts of radiotracers to detect the concentration of relevant biomarkers in tissues such as receptors, enzymes, and transporters
positron emission tomography (PET) radiotracers for the central nervous system (CNS) should have proper pharmacokinetic profile in the brain and to achieve this property, they were designed to meet five molecular properties: (a) molecular weight
None of the reported radiotracers showed promising results for in vivo brain imaging of α1-adrenergic receptors (ARs) for they were limited by poor blood-brain barrier (BBB) penetration, being substrates of Pgp or lack of binding specificity
Summary
Positron emission tomography (PET) is a noninvasive and highly sensitive in vivo imaging technique that uses small amounts of radiotracers to detect the concentration of relevant biomarkers in tissues such as receptors, enzymes, and transporters. None of the reported radiotracers showed promising results for in vivo brain imaging of α1-ARs for they were limited by poor BBB penetration, being substrates of Pgp or lack of binding specificity. In 1997, Pike’s group developed [11 C]RS-15385-197 (10) and [11 C]79948-197 (11) as PET α2-ARs ligands (Figure 2) [89] These radiotracers were prepared from their respective O-desmethyl precursors through the 11 C-methylation method with 61 ± 17 GBq/μmol (10) and 64 ± 3 GBq/μmol molar activity (11). In 2002, Smith’s group developed two tetracyclic based anti-depressant radiotracers, mianserin (13) and mitrazepine (14), that have potent antagonist properties at α2-ARs and at serotonin receptors (5HT2A , 5HT2C ) and labelled them with C-11 to prepare 13 and 14 (Figure 2) [92,93]. Yohimbine has potent antagonist at α2-ARs,properties and interacts with but α1 and antihypertensive agent
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