Alleviation of the chronic stress response attributed to the antioxidant and anti-inflammatory effects of electrolyzed hydrogen water.

Reactive oxygen species (ROS) are highly reactive and directly attack surrounding biomolecules to deteriorate cellular and tissue functions. Meanwhile, ROS also serve as signaling mediators to upregulate pro-inflammatory cytokine expression via activation of the nuclear factor kappa B signaling pathway, and the increased pro-inflammatory cytokines trigger respiratory burst of inflammatory cells that further accelerates ROS production in the inflamed tissue. Such crosstalk between ROS and inflammatory responses leads to a chain reaction of negativity, and cause progression of several chronic pathologies. Since molecular hydrogen is known to preferentially remove cytotoxic hydroxyl radicals and peroxynitrites, and to prevent cell and tissue damage, we here examined whether electrolyzed hydrogen water (EHW) enriched with molecular hydrogen and reactive hydrogen storing platinum nanoparticles dissolved from an electrode could alleviate oxidative stress and inflammation induced by continuous stress challenges. Five-day continuous stress loading to rats elevated reactive oxygen metabolites-derived compounds (d-ROMs), interleukin (IL)-1ß, and adrenocorticotropic hormone (ACTH) levels and decreased the biological antioxidant potential (BAP) level. Drinking EHW during 5-day continuous stress loading significantly alleviated all of these changes. The results suggest that EHW could suppress stress-response-associated oxidative stress and IL-1ß level elevation in vivo, and that drinking of EHW is effective for controlling stress responses via its antioxidant potential.

Synthesis and characterization of 11 C-labeled benzyl amidine derivatives as PET radioligands for GluN2B subunit of the NMDA receptors.

GluN2B-containing NMDA receptors (NMDARs) play fundamental roles in learning and memory, although they are also associated with various brain disorders. In this study, we synthesized and evaluated three 11 C-labeled N-benzyl amidine derivatives 2-[11 C]methoxybenzyl) cinnamamidine ([11 C]CBA), N-(2-[11 C]methoxybenzyl)-2-naphthamidine ([11 C]NBA), and N-(2-[11 C]methoxybenzyl)quinoline-3-carboxamidine ([11 C]QBA) as PET radioligands for these receptors. The 11 C-benzyl amidines were synthesized via conventional methylation of corresponding des-methyl precursors with [11 C]CH3 I. In vitro binding characteristics were examined in brain sagittal sections using various GluN2B modulators and off-target ligands. Further, in vivo brain distribution studies were performed in normal mice. The 11 C-labeled benzyl amidines showed high-specific binding to the GluN2B subunit at in vitro. In particular, the quinoline derivative [11 C]QBA had the best binding properties in terms of high-brain localization to GluN2B-rich regions and specificity to the GluN2B subunit. Conversely, these 11 C-radioligands showed the brain distributions were inconsistent with GluN2B expression in biodistribution experiments. The majority of the radiolabeled compounds were identified as metabolized forms of which amido derivatives seemed to be the major species. Although these 11 C-ligands had high-specific binding to the GluN2B subunit, significant improvement in metabolic stability is necessary for successful positron emission tomography (PET) imaging of the GluN2B subunit of NMDARs.

Extension of recovery time from fatigue by repeated rest with short-term sleep during continuous fatigue load: Development of chronic fatigue model.

Homeostasis is known to be involved in maintaining the optimal internal environment, helping to achieve the best performance of biological functions. At the same time, a deviation from optimal conditions often attenuates the performance of biological functions, and such restricted performance could be considered as individual fatigue, including physical and mental fatigue. The present study seeks to develop an animal model of chronic or subacute fatigue in which the recovery time is extended through the gradual disruption of homeostasis. We show that repeated short-term rest periods with certain lengths of sleep during continuous fatigue loading extend recovery from spontaneous nighttime activity but not physical performance in comparison with a continuous fatigue-loading procedure. Furthermore, the immobility time in a forced swimming test was extended by repeated short-term rests. These results suggest that repeated short-term rest with certain lengths of sleep during continuous fatigue loading is able to extend the recovery from mental fatigue but not from physical fatigue and that this effect might occur via the disruption of a homeostatic mechanism that is involved in restoring the optimal internal environment.

Exploration of Antiemetics for Osteoporosis Therapy-Induced Nausea and Vomiting Using PET Molecular Imaging Analysis to Gastrointestinal Pharmacokinetics.

PURPOSE: To select appropriate antiemetics relieving teriparatide-induced nausea and vomiting during osteoporosis treatment using PET molecular imaging and pharmacokinetic analysis. METHODS: Rats were pretreated with subcutaneous teriparatide, followed by oral administration of antiemetics with different pharmacological effects. The pharmacokinetics of antiemetics were assessed by oral administration of 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) under free moving conditions in vivo. The effect of teriparatide on the permeability of Caco-2 cell membranes to [(18)F]FDG was assessed in vitro. The effects of antiemetics on teriparatide-induced suppression of gastrointestinal motility in vivo was assayed by positron emission tomography (PET) using orally administered [(18)F]FDG. RESULTS: Teriparatide delayed the time-radioactivity profile of [(18)F]FDG in blood and significantly reduced its absorption rate constant (k a ), determined from non-compartmental analysis, to 60% of control. In contrast, co-administration of granisetron or mosapride restored the time-radioactivity profile and k a of [(18)F]FDG to control levels. Teriparatide had no effect on Caco-2 membrane permeability to [(18)F]FDG. Pharmacokinetic PET imaging data analysis quantitatively showed the pharmacological effects of teriparatide-induced suppression of upper gastrointestinal motility and its restoration by granisetron and mosapride. CONCLUSIONS: Teriparatide-induced abdominal discomfort might be attributed to GI motility, and PET imaging analysis is a useful tool to for the selection of appropriate antiemetics.

Quantitative Evaluation of mMate1 Function Based on Minimally Invasive Measurement of Tissue Concentration Using PET with [(11)C]Metformin in Mouse.

PURPOSE: To evaluate the function of multidrug and toxin extrusion proteins (MATEs) using (11)C-labeled metformin ([(11)C]metformin) by positron emission tomography (PET). METHODS: PET was performed by intravenous bolus injection of [(11)C]metformin. Pyrimethamine at 0.5 and 5 mg/kg was intravenously administered to mice 30 min prior to the scan. Integration plot analysis was conducted for calculating liver (CLuptake,liver), kidney (CLuptake,kidney) tissue uptake, intrinsic biliary (CLint,bile) and urinary (CLint,urine) excretion clearances of [(11)C]metformin. RESULTS: Visualization by PET showed that pyrimethamine increased concentrations of [(11)C]metformin in the liver and kidneys, and decreased the concentrations in the urinary bladder without changing the blood profiles. Pyrimethamine had no effect on the CLuptake,liver and CLuptake,kidney, which were similar to the blood-flow rate. CLint,bile with regard to the liver concentration was unable to be determined, but administration of 0.5 and 5 mg/kg of pyrimethamine increased the liver-to-blood ratio to 1.6 and 2.3-fold, respectively, indicating that pyrimethamine inhibited the efflux of [(11)C]metformin from the liver. CLint,urine with regard to the corticomedullary region concentrations was decreased 37 and 68% of the control by administration of 0.5 and 5 mg/kg of pyrimethamine, respectively (P < 0.05). CONCLUSIONS: Tissue concentration based investigations using [(11)C]metformin by PET enables the functional analysis of MATEs in the liver and kidneys.

Evaluation of Oatp and Mrp2 activities in hepatobiliary excretion using newly developed positron emission tomography tracer [11C]dehydropravastatin in rats.

We developed a pravastatin derivative, sodium (3R,5R)-3,5-dihydroxy-7-((1S,2S,6S,8S)-6-hydroxy-2-methyl-8-((1-[(11)C]-(E)-2-methyl-but-2-enoyl)oxy)-1,2,6,7,8,8a-hexahydronaphthalen-1-yl)heptanoate ([(11)C]DPV), as a positron emission tomography (PET) probe for noninvasive measurement of hepatobiliary transport, and conducted pharmacokinetic analysis in rats as a feasibility study for future clinical study. Transport activities of DPV in freshly isolated rat hepatocytes and rodent multidrug resistance-associated protein 2 (rMrp2; human, MRP2)-expressing membrane vesicles were similar to those of pravastatin. Rifampicin diminished the uptake of DPV and pravastatin by the hepatocytes, with similar inhibition potency. [(11)C]DPV underwent biotransformation to produce at least two metabolites in rat, but metabolism of [(11)C]DPV occurred negligibly in human hepatocytes during a 90-minute incubation. After intravenous injection, [(11)C]DPV was mainly distributed to the liver and kidneys, where the tissue uptake clearances (CLuptake,liver and CLuptake,kidney) were blood-flow-limited (73.6 ± 4.8 and 24.6 ± 0.6 ml/min per kilogram, respectively). Systemic elimination of [(11)C]DPV was delayed in rifampicin-treated rat and an Mrp2-deficient mutant rat, Eisai hyperbilirubinemic mutant rat (EHBR). Rifampicin treatment decreased both CLuptake,liver and CLuptake,kidney of [(11)C]DPV by 30% (P < 0.05), whereas these parameters were unchanged in EHBR. Meanwhile, the canalicular efflux clearance (CLint,bile) of [(11)C]DPV, which was 12.2 ± 1.5 ml/min per kilogram in the control rat, decreased by 60% and 89% in rifampicin-treated rat and EHBR (P < 0.05), respectively. These results indicate that [(11)C]DPV is taken up into the liver by organic anion-transporting polypeptides (rodent, Oatps; human, OATP) and excreted into bile by Mrp2 in rat, and that rifampicin may inhibit Mrp2 as well as Oatps, and consequently increase systemic exposure of [(11)C]DPV. PET using [(11)C]DPV is feasible for studies prior to the future clinical investigation of OATP and MRP2 functionality, especially for personalized medicine.

The synthesis and biodistribution of [(11)C]metformin as a PET probe to study hepatobiliary transport mediated by the multi-drug and toxin extrusion transporter 1 (MATE1) in vivo.

In order to develop a new positron emission tomography (PET) probe to study hepatobiliary transport mediated by the multi-drug and toxin extrusion transporter 1 (MATE1), (11)C-labelled metformin was synthesized and then evaluated as a PET probe. [(11)C]Metformin ([(11)C]4) was synthesized in three steps, from [(11)C]methyl iodide. Evaluation by small animal PET of [(11)C]4 showed that there was increased concentrations of [(11)C]4 in the livers of mice pre-treated with pyrimethamine, a potential inhibitor of MATEs, inhibiting the hepatobiliary excretion of metformin. Radiometabolite analysis showed that [(11)C]4 was not degraded in vivo during the PET scan. Biodistribution studies were undertaken and the organ distributions were extrapolated into a standard human model. In conclusion, [(11)C]4 may be useful as a PET probe to non-invasively study the in vivo function of hepatobiliary transport and drug-drug interactions, mediated by MATE1 in future clinical investigations.

In vivo positron emission tomographic imaging of glial responses to amyloid-beta and tau pathologies in mouse models of Alzheimer's disease and related disorders.

Core pathologies of Alzheimer's disease (AD) are aggregated amyloid-ß peptides (Aß) and tau, and the latter is also characteristic of diverse neurodegenerative tauopathies. These amyloid lesions provoke microglial activation, and recent neuroimaging technologies have enabled visualization of this response in living brains using radioligands for the peripheral benzodiazepine receptor also known as the 18 kDa translocator protein (TSPO). Here, we elucidated contributions of Aß and tau deposits to in vivo TSPO signals in pursuit of mechanistic and diagnostic significance of TSPO imaging in AD and other tauopathies. A new antibody to human TSPO revealed induction of TSPO-positive microgliosis by tau fibrils in tauopathy brains. Emergence of TSPO signals before occurrence of brain atrophy and thioflavin-S-positive tau amyloidosis was also demonstrated in living mice transgenic for mutant tau by positron emission tomography (PET) with two classes of TSPO radioligands, [(11)C]AC-5216 and [(18)F]fluoroethoxy-DAA1106. Meanwhile, only modest TSPO elevation was observed in aged mice modeling Aß plaque deposition, despite the notably enhanced in vivo binding of amyloid radiotracer, [(11)C]Pittsburgh Compound-B, to plaques. In these animals, [(11)C]AC-5216 yielded better TSPO contrasts than [(18)F]fluoroethoxy-DAA1106, supporting the possibility of capturing early neurotoxicity with high-performance TSPO probes. Furthermore, an additional line of mice modeling intraneuronal Aß accumulation displayed elevated TSPO signals following noticeable neuronal loss, unlike TSPO upregulation heralding massive neuronal death in tauopathy model mice. Our data corroborate the utility of TSPO-PET imaging as a biomarker for tau-triggered toxicity, and as a complement to amyloid scans for diagnostic assessment of tauopathies with and without Aß pathologies.

N-Methylamide-structured SB366791 derivatives with high TRPV1 antagonistic activity: toward PET radiotracers to visualize TRPV1.

Transient receptor potential cation channel subfamily V member 1 (TRPV1)-targeted compounds were synthesized by modifying the structure of SB366791, a pharmaceutically representative TRPV1 antagonist. To avoid amide-iminol tautomerization, structurally supported N-methylated amides (i.e., 3-alkoxy-substitued N-meythylamide derivatives of SB366791) were evaluated using a Ca2+ influx assay, in which cells expressed recombinant TRPV1 in the presence of 1.0 µM capsaicin. The antagonistic activities of N-(3-methoxyphenyl)-N-methyl-4-chlorocinnamamide (2) (RLC-TV1004) and N-{3-(3-fluoropropoxy)phenyl}-N-methyl-4-chlorocinnamamide (4) (RLC-TV1006) were found to be approximately three-fold higher (IC50: 1.3 µM and 1.1 µM, respectively) than that of SB366791 (IC50: 3.7 µM). These results will help reinvigorate the potential of SB366791 in medicinal chemistry applications. The 3-methoxy and 3-fluoroalkoxy substituents were used to obtain radioactive [11C]methoxy- or [18F]fluoroalkoxy-incorporated tracers for in vivo positron emission tomography (PET). Using the 11C- or 18F-labeled derivatives, explorative PET imaging trials were performed in rats.

In-vivo visualization of key molecular processes involved in Alzheimer's disease pathogenesis: Insights from neuroimaging research in humans and rodent models.

Diverse age-associated neurodegenerative disorders are featured at a molecular level by depositions of self-aggregating molecules, as represented by amyloid beta peptides (Abeta) and tau proteins in Alzheimer's disease, and cascade-type chain reactions are supposedly commenced with biochemical aberrancies of these amyloidogenic components. Mutagenesis and multiplication of the genes encoding Abeta, tau and other pathogenic initiators may accelerate the incipient process at the cascade top, rationalizing generations of transgenic and knock-in animal models of these illnesses. Meanwhile, these genetic manipulations do not necessarily compress the timelines of crucial intermediate events linking amyloidogenesis and neuronal lethality, resulting in an incomplete recapitulation of the diseases. Requirements for modeling the entire cascade can be illustrated by a side-by-side comparison of humans and animal models with the aid of imaging-based biomarkers commonly applicable to different species. Notably, key components in a highly reactive state are assayable by probe-assisted neuroimaging techniques exemplified by positron emission tomography (PET), providing critical information on the in-vivo accessibility of these target molecules. In fact, multispecies PET studies in conjunction with biochemical, electrophysiological and neuropathological tests have revealed putative neurotoxic subspecies of Abeta assemblies, translocator proteins accumulating in aggressive but not neuroprotective microglia, and functionally active neuroreceptors available to endogenous neurotransmitters and exogenous agonistic ligands. Bidirectional translational studies between human cases and model strains based on this experimental paradigm are presently aimed at clarifying the tau pathogenesis, and would be expanded to analyses of disrupted calcium homeostasis and mitochondrial impairments. Since reciprocal causalities among the key processes have indicated an architectural interchangeability between cascade and network connections as an etiological representation, longitudinal imaging assays with manifold probes covering the cascade from top to bottom virtually delineate the network dynamics continuously altering in the course of the disease and its treatment, and therefore expedite the evaluation and optimization of therapeutic strategies intended for suppressing the neurodegenerative pathway over its full length.

In vivo and in vitro imaging of I2 imidazoline receptors in the monkey brain.

I2 imidazoline receptors (I2Rs) are associated with depression, Alzheimer's disease, and Huntington's disease. However, in vivo imaging of I2Rs in the monkey brain has not been reported until now. We performed in vitro and in vivo imaging of (I2Rs) in the monkey brain using ¹¹C-labeled 2-(3-fluoro-4-tolyl)-4,5-dihydro-1H-imidazole ([¹¹C]FTIMD) which has high and selective affinity of I2Rs. In an auto-radiography (ARG) study, the distribution pattern of [¹¹C]FTIMD in the monkey brain was similar to that of [³H]idazoxan binging to I2Rs in the human brain, which was previously described. The specific binding of [¹¹C]FTIMD accounted for >97% of total binding in brain regions existing I2 Rs. In positron emission tomography (PET) studies, the radioactivity was accumulated in brain regions existing I2Rs ligand BU224, the accumulated radioactivity was decreased to approximately 66%-75% of the baseline measurement at 15-45 min after injection of [¹¹C]FTIMD. These results suggest that [¹¹C]FTIMD shows the specific-binging to I2Rs in the monkey brain as depicted by PET and ARG. We performed the first in vivo imaging of I2Rs using [¹¹C]FTIMD in the monkey brain.

Chemogenetic activation of nigrostriatal dopamine neurons in freely moving common marmosets.

To interrogate particular neuronal pathways in nonhuman primates under natural and stress-free conditions, we applied designer receptors exclusively activated by designer drugs (DREADDs) technology to common marmosets. We injected adeno-associated virus vectors expressing the excitatory DREADD hM3Dq into the unilateral substantia nigra (SN) in four marmosets. Using multi-tracer positron emission tomography imaging, we detected DREADD expression in vivo, which was confirmed in nigrostriatal dopamine neurons by immunohistochemistry, as well as by assessed activation of the SN following agonist administration. The marmosets rotated in a contralateral direction relative to the activated side 30-90 min after consuming food containing the highly potent DREADD agonist deschloroclozapine (DCZ) but not on the following days without DCZ. These results indicate that non-invasive and reversible DREADD manipulation will extend the utility of marmosets as a primate model for linking neuronal activity and natural behavior in various contexts.

Neuroimaging and physiological evidence for involvement of glutamatergic transmission in regulation of the striatal dopaminergic system.

Aberrant neurotransmissions via glutamate and dopamine receptors have been the focus of biomedical research on the molecular basis of psychiatric disorders, but the mode of their interaction is yet to be uncovered. In this study, we demonstrated the pharmacological reversal of methamphetamine-stimulated dopaminergic overflow by suppression of group I metabotropic glutamate (mGlu) receptor in living primates and rodents. In vivo positron emission tomography (PET) was conducted on cynomolgus monkeys and rats using a full agonistic tracer for dopamine D(2/3) receptor, [(11)C]MNPA [(R)-2-(11)CH(3)O-N-n-propylnorapomorphine], and fluctuation of kinetic data resulting from anesthesia was avoided by scanning awake subjects. Excessive release of dopamine induced by methamphetamine and abolishment of this alteration by treatment with an antagonist of group I mGlu receptors, 2-methyl-6-(phenylethynyl)pyridine (MPEP), were measured in both species as decreased binding potential because of increased dopamine and its recovery to baseline levels, respectively. Counteraction of MPEP to the methamphetamine-induced dopamine spillover was also supported neurochemically by microdialysis of unanesthetized rat striatum. Moreover, patch-clamp electrophysiological assays using acute brain slices prepared from rats indicated that direct targets of MPEP mechanistically involved in the effects of methamphetamine are present locally within the striatum. Because MPEP alone did not markedly alter the baseline dopaminergic neurotransmission according to our PET and electrophysiological data, the present findings collectively extend the insights on dopamine-glutamate cross talk from extrastriatal localization of responsible mGlu receptors to intrastriatal synergy and support therapeutic interventions in case of disordered striatal dopaminergic status using group I mGlu receptor antagonists assessable by in vivo imaging techniques.

Imaging of peripheral benzodiazepine receptor expression as biomarkers of detrimental versus beneficial glial responses in mouse models of Alzheimer's and other CNS pathologies.

We demonstrate the significance of peripheral benzodiazepine receptor (PBR) imaging in living mouse models of Alzheimer's disease (AD) as biomarkers and functional signatures of glial activation. By radiochemically and immunohistochemically analyzing murine models of the two pathological hallmarks of AD, we found that AD-like Abeta deposition is concurrent with astrocyte-dominant PBR expression, in striking contrast with nonastroglial PBR upregulation in accumulations of AD-like phosphorylated tau. Because tau-induced massive neuronal loss was distinct from the marginal neurodegeneration associated with Abeta plaques in these models, cellular localization of PBR reflected deleterious and beneficial glial reactions to tau versus Abeta pathologies, respectively. This notion was subsequently examined in models of various non-AD neuropathologies, revealing the following reactive glial dynamics underlying differential PBR upregulation: (1) PBR(-) astrogliosis uncoupled with microgliosis or coupled with PBR(+) microgliosis associated with irreversible neuronal insults; and (2) PBR(+) astrogliosis coupled with PBR(- or +/-) microgliosis associated with minimal or reversible neuronal toxicity. Intracranial transplantation of microglia also indicated that nontoxic microglia drives astroglial PBR expression. Moreover, levels of glial cell line-derived neurotrophic factor (GDNF) in astrocytes were correlated with astroglial PBR, except for increased GDNF in PBR(-) astrocytes in the model of AD-like tau pathology, thereby suggesting that PBR upregulation in astrocytes is an indicator of neurotrophic support. Together, PBR expressions in astrocytes and microglia reflect beneficial and deleterious glial reactions, respectively, in diverse neurodegenerative disorders including AD, pointing to new applications of PBR imaging for monitoring the impact of gliosis on the pathogenesis and treatment of AD.

Utility of small-animal positron emission tomographic imaging of rats for preclinical development of drugs acting on the serotonin transporter.

Visualization of neurotransmission components in living small animals using positron emission tomography (PET) has the potential of contributing to the preclinical development of neuroactive drugs, although it is yet to be examined whether quantitative animal PET data on candidate compounds can be extrapolated to humans. Here, we investigated the comparability of the occupancies of serotonin transporter (5-HTT) by therapeutic agents in rat PET studies with our predetermined data from ex- vivo animal experiments and clinical PET scans. Rats were treated with varying doses of fluvoxamine and a newly developed compound, (2S)-1-[4-(3,4-dichlorophenyl) piperidin-1-yl]-3-[2-(5-methyl-1,3,4-oxadiazol-2-yl)benzo[b]furan-4-yloxy]propan-2-ol monohydrochloride (Wf-516), and underwent PET scans with [11C]3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile ([11C]DASB), a selective radioligand for in-vivo quantification of 5-HTT. PET images indicated a reduction of [11C]DASB binding to 5-HTT as a function of the doses and/or plasma concentrations of fluvoxamine and Wf-516. The doses of these drugs at half-maximal effect (15.2 mg/kg and 3.1 mg/kg, respectively), determined that using binding potentials for [11C]DASB, were comparable to those estimated by our previous ex-vivo measurements in rats (4.5 mg/kg and 1.1 mg/kg, respectively), as there was only a 3-fold difference between these results. Moreover, the plasma concentration of fluvoxamine needed for 50% occupancy of central 5-HTT (6.1 ng/ml) was almost equivalent to the value determined in human PET studies (4.6 ng/ml). These findings support the view that the conjunctive use of small-animal PET and [11C]DASB facilitates a quantitative comparison of in-development drugs targeting 5-HTT with established inhibitors and a predictive estimation of their plasma concentrations exerting therapeutic effects in humans.

Development of N-[11C]methylamino 4-hydroxy-2(1H)-quinolone derivatives as PET radioligands for the glycine-binding site of NMDA receptors.

In this study, we synthesized and evaluated several amino 4-hydroxy-2(1H)-quinolone (4HQ) derivatives as new PET radioligand candidates for the glycine site of the NMDA receptors. Among these ligands, we discovered that 7-chloro-4-hydroxy-3-{3-(4-methylaminobenzyl) phenyl}-2-(1H)-quinolone (12) and 5-ethyl-7-chloro-4-hydroxy-3-(3-methylaminophenyl)-2(1H)-quinolone (32) have high affinity for the glycine site (K(i) values; 11.7 nM for 12 and 11.8 nM for 32). In vitro autoradiography experiments indicated that [(11)C]12 and [(11)C]32 showed high specific binding in the brain slices, which were strongly inhibited by both glycine agonists and antagonists. In vivo brain uptake of these (11)C-labeled 4HQs were examined in normal mice. Cerebellum to blood ratio of accumulation, of both [(11)C]12 and [(11)C]32 at 30 min were 0.058, which were slightly higher than those of cerebrum to blood ratio (0.043 and 0.042, respectively). These results indicated that [(11)C]12 and [(11)C]32 have poor blood brain barrier permeability. Although the plasma protein-binding ratio of [(11)C]32 was much lower than methoxy analogs (71% vs 94-98%, respectively), [(11)C]32 still binds with plasma protein strongly. It is conjectured that still acidic moiety and high affinity with plasma protein of [(11)C]32 may prevent in vivo brain uptake. In conclusion, [(11)C]12 and [(11)C]32 are unsuitable for imaging cerebral NMDA receptors.

Longitudinal, quantitative assessment of amyloid, neuroinflammation, and anti-amyloid treatment in a living mouse model of Alzheimer's disease enabled by positron emission tomography.

We provide the first evidence for the capability of a high-resolution positron emission tomographic (PET) imaging system in quantitatively mapping amyloid accumulation in living amyloid precursor protein transgenic (Tg) mice. After the intravenous administration of N-[11C]methyl-2-(4'-methylaminophenyl)-6-hydroxybenzothiazole (or [11C]PIB for "Pittsburgh Compound-B") with high-specific radioactivity, the Tg mice exhibited high-level retention of radioactivity in amyloid-rich regions. PET investigation for Tg mice over an extended range of ages, including longitudinal assessments, demonstrated age-dependent increase in radioligand binding consistent with progressive amyloid accumulation. Reduction in amyloid levels in the hippocampus of Tg mice was also successfully monitored by multiple PET scans along the time course of anti-amyloid treatment using an antibody against amyloid beta peptide (Abeta). Moreover, PET scans with [18F]fluoroethyl-DAA1106, a radiotracer for activated glia, were conducted for these individuals parallel to amyloid imaging, revealing treatment-induced neuroinflammatory responses, the magnitude of which intimately correlated with the levels of pre-existing amyloid estimated by [11C]PIB. It is also noteworthy that the localization and abundance of [11C]PIB autoradiographic signals were closely associated with those of N-terminally truncated and modified Abeta, AbetaN3-pyroglutamate, in Alzheimer's disease (AD) and Tg mouse brains, implying that the detectability of amyloid by [11C]PIB positron emission tomography is dependent on the accumulation of specific Abeta subtypes. Our results support the usefulness of the small animal-dedicated PET system in conjunction with high-specific radioactivity probes and appropriate Tg models not only for clarifying the mechanistic properties of amyloidogenesis in mouse models but also for preclinical tests of emerging diagnostic and therapeutic approaches to AD.

Neurobehavioral protection by single dose l-deprenyl against MPTP-induced parkinsonism in common marmosets.

OBJECTIVE: Establishment of preclinical method evaluating behavioral protective actions of drugs for Parkinson's disease was attempted using l-deprenyl (DEP) as a reference drug in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-treated common marmosets. MATERIALS AND METHODS: Fifteen marmosets received MPTP at 2 mg/kg, subcutaneously (s.c.) per day for three consecutive days. To these marmosets, intragastric (i.g.) administration of DEP at 10 mg/kg was pretreated 2 h before each MPTP administration in DEP3 group and pretreated only in the first MPTP administration day in DEP1 group. As a control, distilled water (DW) was pretreated before each MPTP administration (n = 5 for each of three groups). RESULTS: In DW group, decreased daily activity counts and increased dysfunction scores were persistently observed for 3 weeks after MPTP. In DEP groups, the similar changes of both levels to those in DW group were temporally observed after MPTP for several days and then the values recovered to the pre-MPTP levels. The results of autoradiography performed after above behavioral observations indicated that markedly lower bindings of [(11)C]PE2I (ligand for dopamine transporters) were observed at the striatum of DW group marmoset as compared with the striatum of additionally prepared MPTP-free marmoset (n = 5). The bindings in DEP groups were almost the same as in the MPTP-free marmoset brains. CONCLUSION: The present preclinical methods using continuous recording of activity of marmosets in their living cages and autoradiography using dopamine transporter ligand might be sensitive for detecting protective actions of drugs for Parkinson's disease.

Difference in brain distributions of carbon 11-labeled 4-hydroxy-2(1H)-quinolones as PET radioligands for the glycine-binding site of the NMDA ion channel.

High-affinity iodine- and ethyl-C-5 substituted analogs of 4-hydroxy-3-(3-[11C]methoxyphenyl)-2(1H)-quinolone ([11C]4HQ) were synthesized as new positron emission tomography radioligands for the glycine-binding sites of the N-methyl-d-aspartate (NMDA) ion channel. Although both radioligands showed high in vitro specific binding to rat brain slices, their binding characteristics were quite different from each other. 5-Ethyl-[11C]4HQ (5Et-[11C]4HQ) showed higher in vitro binding in the forebrain regions than in the cerebellum, bindings that were strongly inhibited by both glycine-site agonists and antagonists. In contrast, 5-iodo-[11C]4HQ (5I-[11C]4HQ) showed a homogeneous in vitro binding throughout the brain, which was inhibited by antagonists but not by agonists. This difference in in vitro binding between 5Et-[11C]4HQ and 5I-[11C]4HQ was quite similar to that previously observed between [11C]L-703,717 and [11C]4HQ, both glycine-site antagonists. In vivo brain uptakes of these 11C-labeled 4-hydroxyquinolones were examined in mice. Initial brain uptakes of 5Et- and 5I-[11C]4HQ at 1 min after intravenous injections were comparable to that of [11C]4HQ, but they were 1.3-2.1 times higher than that of [11C]L-703,717. The treatment with an anticoagulant, warfarin, only slightly increased the initial uptakes of [11C]4HQ and 5Et-[11C]4HQ in contrast to [11C]L-703,717. The in vivo regional brain distributions were slightly different between the two radioligands. Pretreatment with nonradioactive ligand (2 mg/kg) slightly inhibited the binding of 5Et-[11C]4HQ (16-36% inhibition) but not that of 5I-[11C]4HQ. In this study, it was found that a small structural change in [11C]4HQ resulted in a major change in binding characteristics and distributions, suggesting the existence of two binding sites for [11C]4-hydroxyquinolones on the NMDA ion channel - agonist-sensitive and agonist-insensitive (or antagonist-preferring) sites.