Katsuhiko Shibuya

Positron emission tomography evaluation of sedative properties of antihistamines

Introduction: H1 antihistamines are often used in the medication for allergic diseases, coughs and colds, and insomnia, with or without prescription, even though their sedative properties are a potentially dangerous unwanted side effect that is not properly recognized. These sedative properties have been evaluated using the incidence of subjective sleepiness, objective cognitive and psychomotor functions, and positron emission tomography (PET) measurement of H1 receptor occupancy. Areas covered: This article reviews the current updated literature on the sedative properties of antihistamines examined by PET measurement of H1 receptor occupancy. Expert opinion: The use of PET to examine antihistamine penetration in the human brain in relation to psychometric and other functional measures of CNS effects is a major breakthrough and provides a new standard by which the functional CNS effects of antihistamines can be related directly to H1 receptor occupancy. Therapy with antihistamines can be better guided by considering histamine H1 receptor occupancy from the view of their sedative properties.

Mechanism of the histamine H3 receptor-mediated increase in exploratory locomotor activity and anxiety-like behaviours in mice

Histaminergic neurons are activated by histamine H(3) receptor (H(3)R) antagonists, increasing histamine and other neurotransmitters in the brain. The prototype H(3)R antagonist thioperamide increases locomotor activity and anxiety-like behaviours; however, the mechanisms underlying these effects have not been fully elucidated. This study aimed to determine the mechanism underlying H(3)R-mediated behavioural changes using a specific H(3)R antagonist, JNJ-10181457 (JNJ). First, we examined the effect of JNJ injection to mice on the concentrations of brain monoamines and their metabolites. JNJ exclusively increased N(τ)-methylhistamine, the metabolite of brain histamine used as an indicator of histamine release, suggesting that JNJ dominantly stimulates the release of histamine release but not of other monoamines. Next, we examined the mechanism underlying JNJ-induced behavioural changes using open-field tests and elevated zero maze tests. JNJ-induced increase in locomotor activity was inhibited by α-fluoromethyl histidine, an inhibitor of histamine synthesis, supporting that H(3)R exerted its effect through histamine neurotransmission. The JNJ-induced increase in locomotor activity in wild-type mice was preserved in H(1)R gene knockout mice but not in histamine H2 receptor (H(2)R) gene knockout mice. JNJ-induced anxiety-like behaviours were partially reduced by diphenhydramine, an H(1)R antagonist, and dominantly by zolantidine, an H(2)R antagonist. These results suggest that H(3)R blockade induces histamine release, activates H(2)R and elicits exploratory locomotor activity and anxiety-like behaviours.

[11C]Doxepin binding to histamine H1 receptors in living human brain: reproducibility during attentive waking and circadian rhythm

Molecular imaging in neuroscience is a new research field that enables visualization of the impact of molecular events on brain structure and function in humans. While magnetic resonance-based imaging techniques can provide complex information at the level of system, positron emission tomography (PET) enables determination of the distribution and density of receptor and enzyme in the human brain. Previous studies using [11C]raclopride and [11C]FLB457 revealed that the release of neuronal dopamine was increased in human brain by psychostimulants or reward stimuli. Following on from these previous [11C]raclopride studies, we examined whether the levels of neuronal release of histamine might change [11C]doxepin binding to the H1 receptors under the influence of physiological stimuli. The purpose of the present study was to evaluate the test–retest reliability of quantitative measurement of [11C]doxepin binding between morning and afternoon and between resting and attentive waking conditions in healthy human subjects. There was a trend for a decrease in [11C]doxepin binding during attentive calculation tasks compared with that in resting conditions, but the difference (less than 10%) was not significant. Similarly, the binding potential of [11C]doxepin in the cerebral cortex was slightly higher in the morning than that in the afternoon, but it was also insignificant. These data suggest that higher histamine release during wakefulness could not decrease the [11C]doxepin binding in the brain. This study confirmed the reproducibility and reliability of [11C]doxepin in the previous imaging studies to measure the H1 receptor.

Synthesis and Characterization of 18F-Interleukin-8 Using a Cell-Free Translation System and 4-18F-Fluoro-l-Proline

Macromolecules such as proteins are attracting increasing interest for molecular imaging. We previously proposed a novel strategy for preparing macromolecules labeled with a PET radionuclide, 11C, using a cell-free translation system with 11C-methionine. However, macromolecules tend to exhibit slower kinetics, thus requiring a longer scanning time. Here, we expand our strategy using 18F, which has a longer half-life, with the cell-free translation system with 4-18F-fluoro-l-proline (18F-FPro). We evaluated 18F-interleukin-8 (18F-IL-8) produced by this method in vitro and in vivo to provide a proof of concept of our strategy. Methods: We tested some fluorinated amino acids to be incorporated into a protein. Trans-18F-FPro was radiolabeled from the corresponding precursor. 18F-IL-8 was produced using the cell-free translation system with trans-18F-FPro instead of natural l-proline with incubation at 37°C for 120 min. An in vitro binding assay of 18F-IL-8 was performed using IL-8 receptor–expressing cells. After intravenous administration of 18F-IL-8, in vivo PET imaging of IL-8 receptor–expressing xenograft-bearing mice was performed using a small-animal PET system. Results: FPro was identified as an amino acid incorporated into the protein. 18F-IL-8 was successfully prepared using the cell-free translation system and trans-18F-FPro with the radiochemical yield of 1.5% (decay-corrected) based on trans-18F-FPro. In vitro binding assays of 18F-IL-8 demonstrated its binding to IL-8 receptor. In vivo PET imaging demonstrated that 18F-IL-8 clearly accumulated in IL-8 receptor–expressing xenografts in mice, unlike trans-18F-FPro. Conclusion: 18F-IL-8 produced by this method binds to IL-8 receptors in vitro, and 18F-IL-8 PET clearly visualizes its target receptor–expressing xenograft in vivo. Therefore, this technique might be useful for labeling macromolecules and performing preclinical evaluations of proteins of interest in vitro and in vivo.

Synthesis of [11C]interleukin 8 using a cell-free translation system and L-[11C]methionine.

Positron emission tomography (PET), which requires a compound labeled with a positron emitter radioisotope as an imaging probe, is one of the most useful and valuable imaging modalities in molecular imaging. It has several advantages over other imaging modalities, particularly in sensitive and quantitative investigations of molecular functions and processes in vivo. Recent advances in biopharmaceuticals development have increased interest in practical methods for proteins and peptides labeling with positron emitter radioisotope for PET molecular imaging. Here, we propose a novel approach for preparing positron emitter-labeled proteins and peptides based on biochemical synthesis using a reconstituted cell-free translation system. In this study, [(11)C]interleukin 8 (IL-8; MW 9.2 kDa) was successfully synthesized by the cell-free system in combination with l-[(11)C]methionine. The in vitro biochemical reaction proceeded smoothly and gave maximum radioactivity of [(11)C]IL-8 at 20 min with a radiochemical yield of 63%. Purification of [(11)C]IL-8 was achieved by conventional cation exchange and ultrafiltration methods, resulting in enough amount of radioactivity with excellent radiochemical purity (>95%) for small-animal imaging. This study clearly demonstrates that cell-free protein production system combined with positron emitter-labeled amino acid holds great promise as a novel approach to prepare radiolabeled proteins and peptides for PET imaging.

Glucose Metabolic Changes in the Brain and Muscles of Patients with Nonspecific Neck Pain Treated by Spinal Manipulation Therapy: A [18F]FDG PET Study

Objective. The aim of this study was to investigate changes in brain and muscle glucose metabolism that are not yet known, using positron emission tomography with [18F]fluorodeoxyglucose ([18F]FDG PET). Methods. Twenty-one male volunteers were recruited for the present study. [18F]FDG PET scanning was performed twice on each subject: once after the spinal manipulation therapy (SMT) intervention (treatment condition) and once after resting (control condition). We performed the SMT intervention using an adjustment device. Glucose metabolism of the brain and skeletal muscles was measured and compared between the two conditions. In addition, we measured salivary amylase level as an index of autonomic nervous system (ANS) activity, as well as muscle tension and subjective pain intensity in each subject. Results. Changes in brain activity after SMT included activation of the dorsal anterior cingulate cortex, cerebellar vermis, and somatosensory association cortex and deactivation of the prefrontal cortex and temporal sites. Glucose uptake in skeletal muscles showed a trend toward decreased metabolism after SMT, although the difference was not significant. Other measurements indicated relaxation of cervical muscle tension, decrease in salivary amylase level (suppression of sympathetic nerve activity), and pain relief after SMT. Conclusion. Brain processing after SMT may lead to physiological relaxation via a decrease in sympathetic nerve activity.

The acute blockade of histamine H3 receptors increases anxiogenic-like behaviors in mice

outgrowth by As. In contrast to the striking effect on neurite outgrowth, overexpression of GluR2 could not rescue the mortality of neurons in the culture at concentration above 2 M As. These results suggest the possibility that suppression of neurite outgrowth by As in primary cortical neurons occurs through impact on glutamate transmission, which might be independent of the effect on cell death. Research fund: Supported by National Institute for environmental studies (0406AG337).

Quantitative Analysis of Amyloid Beta Deposition in the Brain of Alzheimer’s Disease Patients Using PET and [11C]BF-227 and [18F]FACT

In vivo detection of amyloid deposits is useful for early diagnosis of Alzheimer’s disease (AD) and for prediction of potential converters from mild cognitive impairment (MCI) to AD. Our original imaging probe, [11C]BF-227, has been shown to be useful for clinical evaluation of AD, MCI and various neurodegenerative disorders using positron emission tomography (PET). Purpose of the present study is to examine methods for quantitative analysis of amyloid deposition in human brain using PET and [11C]BF-227 as well as our newer compound [18F]FACT.