Dopamine Response to Psychosocial Stress in Chronic Cannabis Users: A PET Study With [11C]-(+)-PHNO

A number of addictions have been linked with decreased striatal dopamine (DA) receptor availability and DA release. Stress has a key role in cannabis craving, as well as in modulation of dopaminergic signaling. The present study aimed to assess DA release in response to a laboratory stress task with [¹¹C]-(+)-PHNO positron emission tomography in cannabis users (CU). Thirteen healthy CU and 12 healthy volunteers (HV) were scanned during a sensorimotor control task (SMCT) and under a stress condition using the validated Montreal imaging stress task (MIST). The simplified reference tissue model (SRTM) was used to obtain binding potential (BP_ND) in striatal subdivisions: limbic striatum (LST), associative striatum (AST), and sensorimotor striatum (SMST). Stress-induced DA release (indexed as a percentage of reduction in [¹¹C]-(+)-PHNO BP _ND) between CU and HV was tested with analysis of variance. SMCT BP_ND was significantly higher in CU compared with HV in the AST (F=10.38, p=0.003), LST (F=4.95, p=0.036), SMST (F=4.33, p=0.048), and whole striatum (F=9.02, p=0.006). Percentage of displacement (change in BP_ND between SMCT and MIST PET scans) was not significantly different across groups in any brain region, except in the GP (−5.03±14.6 in CU, compared with 6.15±12.1 in HV; F=4.39, p=0.049). Duration of cannabis use was significantly associated with stress-induced [¹¹C]-(+)-PHNO displacement by endogenous DA in the LST (r=0.566, p=0.044), with no effect in any other brain region. In conclusion, despite an increase in striatal BP_ND observed during the control task, chronic cannabis use is not associated with alterations in stress-induced DA release.     

Heightened D3 Dopamine Receptor Levels in Cocaine Dependence and Contributions to the Addiction Behavioral Phenotype: A Positron Emission Tomography Study with [11C]-(+)-PHNO

The dopamine system is a primary treatment target for cocaine dependence (CD), but research on dopaminergic abnormalities (eg, D₂ receptor system deficiencies) has so far failed to translate into effective treatment strategies. The D₃ receptor system has recently attracted considerable clinical interest, and D₃ antagonism is now under investigation as a novel avenue for addiction treatment. The objective here was to evaluate the status and behavioral relevance of the D₃ receptor system in CD, using the positron emission tomography (PET) radiotracer [¹¹C]-(+)-PHNO. Fifteen CD subjects (many actively using, but all abstinent 7–240 days on scan day) and fifteen matched healthy control (HC) subjects completed two PET scans: one with [¹¹C]-(+)-PHNO to assess D₃ receptor binding (BP_ND; calculated regionally using the simplified reference tissue model), and for comparison, a second scan with [¹¹C]raclopride to assess D_2/3 binding. CD subjects also completed a behavioral battery to characterize the addiction behavioral phenotype. CD subjects showed higher [¹¹C]-(+)-PHNO BP_ND than HC in the substantia nigra, which correlated with behavioral impulsiveness and risky decision making. In contrast, [¹¹C]raclopride BP_ND was lower across the striatum in CD, consistent with previous literature in ⩾2 week abstinence. The data suggest that in contrast to a D₂ deficiency, CD individuals may have heightened D₃ receptor levels, which could contribute to addiction-relevant traits. D₃ upregulation is emerging as a biomarker in preclinical models of addiction, and human PET studies of this receptor system can help guide novel pharmacological strategies for treatment.     

The Antipsychotics Olanzapine, Risperidone, Clozapine, and Haloperidol Are D2-Selective Ex Vivo but Not In Vitro

In a recent human [¹¹C]-(+)-PHNO positron emission tomography study, olanzapine, clozapine, and risperidone occupied D2 receptors in striatum (STR), but, despite their similar in vitro D2 and D3 affinities, failed to occupy D3 receptors in globus pallidus. This study had two aims: (1) to characterize the regional D2/D3 pharmacology of in vitro and ex vivo [³H]-(+)-PHNO binding sites in rat brain and (2) to compare, using [³H]-(+)-PHNO autoradiography, the ex vivo and in vitro pharmacology of olanzapine, clozapine, risperidone, and haloperidol. Using the D3-selective drug SB277011, we found that ex vivo and in vitro [³H]-(+)-PHNO binding in STR is exclusively due to D2, whereas that in cerebellar lobes 9 and 10 is exclusively due to D3. Surprisingly, the D3 contribution to [³H]-(+)-PHNO binding in the islands of Calleja, ventral pallidum, substantia nigra, and nucleus accumbens was greater ex vivo than in vitro. Ex vivo, systemically administered olanzapine, risperidone, and haloperidol, at doses occupying ∼80% D2, did not occupy D3 receptors. Clozapine, which also occupied ∼80% of D2 receptors ex vivo, occupied a smaller percentage of D3 receptors than predicted by its in vitro pharmacology. Across brain regions, ex vivo occupancy by antipsychotics was inversely related to the D3 contribution to [³H]-(+)-PHNO binding. In contrast, in vitro occupancy was similar across brain regions, independent of the regional D3 contribution. These data indicate that at clinically relevant doses, olanzapine, clozapine, risperidone, and haloperidol are D2-selective ex vivo. This unforeseen finding suggests that their clinical effects cannot be attributed to D3 receptor blockade.     

Imaging Nicotine- and Amphetamine-Induced Dopamine Release in Rhesus Monkeys with [11C]PHNO vs [11C]raclopride PET

The radiotracer [¹¹C]PHNO may have advantages over other dopamine (DA) D₂/D₃ receptor ligands because, as an agonist, it measures high-affinity, functionally active D₂/D₃ receptors, whereas the traditionally used radiotracer [¹¹C]raclopride measures both high- and low-affinity receptors. Our aim was to take advantage of the strength of [¹¹C]PHNO for measuring the small DA signal induced by nicotine, which has been difficult to measure in preclinical and clinical neuroimaging studies. Nicotine- and amphetamine-induced DA release in non-human primates was measured with [¹¹C]PHNO and [¹¹C]raclopride positron emission tomography (PET) imaging. Seven adult rhesus monkeys were imaged on a FOCUS 220 PET scanner after injection of a bolus of [¹¹C]PHNO or [¹¹C]raclopride in three conditions: baseline; preinjection of nicotine (0.1 mg/kg bolus+0.08 mg/kg infusion over 30 min); preinjection of amphetamine (0.4 mg/kg, 5 min before radiotracer injection). DA release was measured as change in binding potential (BP_ND). Nicotine significantly decreased BP_ND in the caudate (7±8%), the nucleus accumbens (10±7%), and in the globus pallidus (13±15%) measured with [¹¹C]PHNO, but did not significantly decrease BP_ND in the putamen or the substantia nigra or in any region when measured with [¹¹C]raclopride. Amphetamine significantly reduced BP_ND in all regions with both radiotracers. In the striatum, larger amphetamine-induced changes were detected with [¹¹C]PHNO compared with [¹¹C]raclopride (52–64% vs 33–35%, respectively). We confirmed that [¹¹C]PHNO is more sensitive than [¹¹C]raclopride to nicotine- and amphetamine-induced DA release. [¹¹C]PHNO PET may be more sensitive to measuring tobacco smoking-induced DA release in human tobacco smokers.     

Amphetamine-Induced Dopamine Release and Neurocognitive Function in Treatment-Naive Adults with ADHD

Converging evidence from clinical, preclinical, neuroimaging, and genetic research implicates dopamine neurotransmission in the pathophysiology of attention deficit hyperactivity disorder (ADHD). The in vivo neuroreceptor imaging evidence also suggests alterations in the dopamine system in ADHD; however, the nature and behavioral significance of those have not yet been established. Here, we investigated striatal dopaminergic function in ADHD using [¹¹C]raclopride PET with a d-amphetamine challenge. We also examined the relationship of striatal dopamine responses to ADHD symptoms and neurocognitive function. A total of 15 treatment-free, noncomorbid adult males with ADHD (age: 29.87±8.65) and 18 healthy male controls (age: 25.44±6.77) underwent two PET scans: one following a lactose placebo and the other following d-amphetamine (0.3 mg/kg, p.o.), administered double blind and in random order counterbalanced across groups. In a separate session without a drug, participants performed a battery of neurocognitive tests. Relative to the healthy controls, the ADHD patients, as a group, showed greater d-amphetamine-induced decreases in striatal [¹¹C]raclopride binding and performed more poorly on measures of response inhibition. Across groups, a greater magnitude of d-amphetamine-induced change in [¹¹C]raclopride binding potential was associated with poorer performance on measures of response inhibition and ADHD symptoms. Our findings suggest an augmented striatal dopaminergic response in treatment-naive ADHD. Though in contrast to results of a previous study, this finding appears consistent with a model proposing exaggerated phasic dopamine release in ADHD. A susceptibility to increased phasic dopamine responsivity may contribute to such characteristics of ADHD as poor inhibition and impulsivity.     

Higher Levels of Glutamate in the Associative-Striatum of Subjects with Prodromal Symptoms of Schizophrenia and Patients with First-Episode Psychosis

The glutamatergic and dopaminergic systems are thought to be involved in the pathophysiology of schizophrenia. Their interaction has been widely documented and may have a role in the neurobiological basis of the disease. The aim of this study was to compare, using proton magnetic resonance spectroscopy (¹H-MRS), glutamate levels in the precommissural dorsal-caudate (a dopamine-rich region) and the cerebellar cortex (negligible for dopamine) in the following: (1) 18 antipsychotic-naïve subjects with prodromal symptoms and considered to be at ultra high-risk for schizophrenia (UHR), (2) 18 antipsychotic-naïve first- episode psychosis patients (FEP), and (3) 40 age- and sex- matched healthy controls. All subjects underwent a ¹H-MRS study using a 3Tesla scanner. Glutamate levels were quantified and corrected for the proportion of cerebrospinal fluid and percentage of gray matter in the voxel. The UHR and FEP groups showed higher levels of glutamate than controls, without differences between UHR and FEP. In the cerebellum, no differences were seen between the three groups. The higher glutamate level in the precommissural dorsal-caudate and not in the cerebellum of UHR and FEP suggests that a high glutamate level (a) precedes the onset of schizophrenia, and (b) is present in a dopamine-rich region previously implicated in the pathophysiology of schizophrenia.     

Cortico-Striatal GABAergic and Glutamatergic Dysregulations in Subjects at Ultra-High Risk for Psychosis Investigated with Proton Magnetic Resonance Spectroscopy

Background:

Dysregulations of the major inhibitory and excitatory amino neurotransmitter systems of γ-aminobutyric acid and glutamate, respectively, have been described in patients with schizophrenia. However, it is unclear whether these abnormalities are present in subjects at ultra-high risk for psychosis.

Methods:

Twenty-three antipsychotic naïve subjects at ultra-high risk and 24 healthy control subjects, matched for age, sex, handedness, cigarette smoking, and parental education, underwent proton magnetic resonance spectroscopy scans in the dorsal caudate bilaterally and the medial prefrontal cortex at 3T. Levels of γ-aminobutyric acid and of the combined resonance of glutamate and glutamine (Glx) were obtained using the standard J-editing technique and expressed as peak area ratios relative to the synchronously acquired unsuppressed voxel water signal.

Results:

Higher levels of γ-aminobutyric acid (P<.001) and Glx (P=.007) were found in the dorsal caudate of the subjects at ultra-high risk than in the healthy controls. In the medial prefrontal cortex, likewise, both γ-aminobutyric acid (P=.03) and Glx (P=.006) levels were higher in the ultra-high risk group than in the healthy controls. No group differences were found for any of the other metabolites (N-acetylaspartate, total choline, or total creatine) in the 2 regions of interest.

Conclusions:

This study presents the first evidence of abnormal elevations, in subjects at ultra-high risk, of γ-aminobutyric acid and Glx in 2 brain regions that have been implicated in the pathophysiology of psychosis, warranting longitudinal studies to assess whether these neurotransmitter abnormalities can serve as noninvasive biomarkers of conversion risk to psychosis as well as of illness progression and treatment response.     

Sustained Recreational Use of Ecstasy Is Associated with Altered Pre and Postsynaptic Markers of Serotonin Transmission in Neocortical Areas: A PET Study with [11C]DASB and [11C]MDL 100907

3,4-Methylenedioxymethamphetamine (MDMA), the main psychoactive component of the recreational drug ecstasy, is a potent serotonin (5-HT) releaser. In animals, MDMA induces 5-HT depletion and toxicity in 5-HT neurons. The aim of this study was to investigate both presynaptic (5-HT transporter, SERT) and postsynaptic (5-HT_2A receptor) markers of 5-HT transmission in recently abstinent chronic MDMA users compared with matched healthy controls. We hypothesized that MDMA use is associated with lower SERT density and concomitant upregulation of 5-HT_2A receptors. Positron emission tomography studies using the SERT ligand [¹¹C]DASB and the 5-HT_2A receptor ligand [¹¹C]MDL 100907 were evaluated in 13 current and recently detoxified MDMA users and 13 matched healthy controls. MDMA users reported a mean duration of ecstasy use of 8 years, regular exposure, and at least 2 weeks of abstinence before the scans. SERT and 5-HT_2A receptor availability (binding potential, BP_ND) were analyzed with a two-tissue compartment model with arterial input function. Current recreational MDMA use was significantly associated with lower SERT BP_ND and higher 5-HT_2A receptor BP_ND in cortical, but not subcortical regions. Decreased SERT BP_ND was regionally associated with upregulated 5-HT_2A receptor BP_ND. In light of the animal literature, the most parsimonious interpretation is that repeated exposure to MDMA in humans, even in moderate amounts, leads to damage in 5-HT neuron terminals innervating the cortex. Alterations in mood, cognition, and impulse control associated with these changes might contribute to sustain MDMA use. The reversibility of these changes upon abstinence remains to be firmly established.     

Incongruent Reduction of Serotonin Transporter Associated with Suicide Attempts in Patients with Major Depressive Disorder: A Positron Emission Tomography Study with 4-[18F]-ADAM

Background:

Much evidence supports the role of the serotonin transporter (SERT) in the pathophysiology and pharmacotherapy of major depressive disorder (MDD) and suicidal behaviors.

Methods:

In this study, we recruited 17 antidepressant-naïve patients with MDD and 17 age- and gender-matched healthy controls. SERT availability was measured in vivo with N,N-dimethyl-2-(2-amino-4-[¹⁸F]fluorophenylthio)benzylamine (4-[¹⁸F]-ADAM) positron emission tomography (PET) imaging. The 21-item Hamilton Depression Rating Scale (HDRS) and Beck Scale for Suicide Ideation were used to assess the severity of depression and the intent of suicide ideation prior to PET imaging. All subjects with MDD were in a current state of depression with HDRS scores ≧18. Subjects who attempted suicide within two weeks of the study onset were recruited in the depressed suicidal group (n = 8). Subjects with MDD who denied any prior suicide attempt were recruited into the depressed non-suicidal group (n = 9).

Results:

A significant reduction of SERT availability in the midbrain, thalamus, and striatum was noted in the MDD group relative to the control group (Bonferroni-adjusted p-value < 0.05). Moreover, this effect was more pronounced in the depressed suicidal group compared to the control group (Bonferroni-adjusted p-value < 0.01). Relative to both the depressed non-suicidal and control groups, the depressed suicidal group showed an increased prefrontal cortex (PFC)/midbrain SERT binding ratio (Bonferroni-adjusted p-value < 0.01).

Conclusions:

This study suggests an incongruent reduction of PFC SERT binding relative to the midbrain might discriminate between depressed suicide attempters and non-attempters in patients with MDD and may be involved in the pathophysiology of suicide behaviors.     

A Novel α5GABAAR-Positive Allosteric Modulator Reverses Hyperactivation of the Dopamine System in the MAM Model of Schizophrenia

We have shown previously that aberrant hippocampal (HPC) output underlies the dopamine (DA) dysfunction observed in the methylazoxymethanol acetate (MAM) developmental model of schizophrenia in the rodent. This alteration of HPC activity was proposed to result from a reduction in parvalbumin (PV)-expressing GABAergic interneurons and consequent destabilization of the output of pyramidal neurons, as well as disrupted activation across a broad neural network. In vivo extracellular recordings were performed in the ventral tegmental area (VTA) and ventral HPC of saline- (SAL) and MAM-treated animals. A novel benzodiazepine-positive allosteric modulator (PAM), selective for the α5 subunit of the GABA_A receptor, SH-053-2′F-R-CH3, was tested for its effects on the output of the HPC, leading to dopamine system hyperactivity in MAM-treated animals. In addition, the effect of SH-053-2′F-R-CH3 on the hyperactive locomotor response to amphetamine in MAM animals was examined. We demonstrate that treatment with the α5GABA_AR PAM reduced the number of spontaneously active DA neurons in the VTA of MAM animals to levels observed in SAL rats, both when administered systemically and when directly infused into the ventral HPC. Moreover, HPC neurons in both SAL and MAM animals showed diminished cortical-evoked responses following α5GABA_AR PAM treatment. In addition, the increased locomotor response to amphetamine observed in MAM rats was reduced following α5GABA_AR treatment. This study supports a novel treatment of schizophrenia that targets abnormal HPC output, which in turn normalizes dopaminergic neuronal activity.     

Age dependency of cerebral P-gp function measured with (<Emphasis Type="Italic">R</Emphasis>)-[<Superscript>11</Superscript>C]verapamil and PET

Purpose  The aim of this study was to assess the influence of age on the functional activity of the multidrug efflux transporter P-glycoprotein (P-gp) at the human blood-brain barrier. Methods  Seven young (mean age: 27 ± 4 years) and six elderly (mean age: 69 ± 9 years) healthy volunteers underwent dynamic (R)-[¹¹C]verapamil (VPM) positron emission tomography (PET) scans and arterial blood sampling. Parametric distribution volume (DV) images were generated using Logan linearisation, and age groups were compared with statistical parametric mapping (SPM). Brain regions that SPM analysis had shown to be most affected by age were analysed by a region of interest (ROI)-based approach using a maximum probability brain atlas, before and after partial volume correction (PVC). Results  SPM analysis revealed significant clusters of DV increases in cerebellum, temporal and frontal lobe of elderly compared to younger subjects. In the ROI-based analysis, elderly subjects showed significant DV increases in amygdala (+30%), insula (+26%) and cerebellum (+25%) before PVC, and in insula (+33%) after PVC. Conclusions  Increased VPM DV values in the brains of elderly subjects suggest a decrease in cerebral P-gp function with increasing age.     

Construction of a Whole Body Blood Flow Model for Use in Positron Emission Tomography Imaging with [15O]Water

A whole body blood flow model (WBBFM) was developed and tested using STELLA II, an icon-driven mathematical simulation software package. The WBBFM uses parallel chambers to represent gray and white areas of the brain, body organs such as lungs, heart (right and left halves), injection site, and blood sampling sites. Input values to the WBBFM include organ blood flows, organ volumes, tissue:blood partition coefficients, injected activity, and data acquisition times for a positron emission tomography (PET) camera. Input variables included an injection function (e.g., bolus), and a blood flow function (e.g., transient variations in flow). The kinetic behavior of [ ¹⁵ O]water, a freely diffusible radiotracer employed in PET to characterize blood flow was examined by the WBBFM. The physiologic behavior of water in the human body was emulated using the WBBFM and the model's predictive value was verified by comparing calculated results with the following properties of water: diffusibility, tissue:blood partition coefficient of [ ¹⁵ O]water, and the mixing of [ ¹⁵ O]water with total body water. The WBBFM simulated Kety's autoradiographic method used in the estimation of regional cerebral blood flow by PET using [ ¹⁵ O]water. The application of the model to a cognitive activation study paradigm based on Kety's method is presented and its results compared to published literature data. With appropriate modification in the half-life, tissue:blood partition coefficient, and the amount of administered radioactivity, the WBBFM should prove useful us a tool to examine kinetics of other freely diffusible radiotracers used in PET.     

A Novel Mechanism of Cocaine to Enhance Dopamine D2-Like Receptor Mediated Neurochemical and Behavioral Effects. An In Vivo and In Vitro Study

Recent in vitro results suggest that cocaine may exert direct and/or indirect allosteric enhancing actions at dopamine (DA) D₂ receptors (D₂Rs). In the present paper we tested the hypothesis that cocaine in vivo can enhance the effects of the D₂-likeR agonist quinpirole in rats by using microdialysis and pharmacological behavioral studies. Furthermore, in vitro D₂-likeR binding characteristics and Gα_i/o-protein coupling, in the absence and in the presence of cocaine, have been investigated in rat striatal membranes. Intra-nucleus accumbens perfusion of the D₂-likeR agonist quinpirole (10 μM) reduced local dialysate glutamate levels, whereas cocaine (10 and 100 nM) was ineffective. At a low concentration (100 nM), cocaine significantly enhanced quinpirole-induced reduction of accumbal extracellular glutamate levels. The behavioral experiments showed that cocaine (0.625 mg/kg), but not the DA uptake blocker GBR 12783 (1.25 mg/kg), enhanced quinpirole (1 mg/kg)-induced hyperlocomotion. Finally, cocaine (100 nM), but not GBR 12783 (200 nM), produced a small, but significant increase in the efficacy of DA to stimulate binding of GTPγS to striatal D₂-likeRs, whereas the D₂-likeR binding characteristics were unchanged in striatal membranes by cocaine in the nM range. The significant increase in the maximal response to DA-stimulated GTPγS binding to D₂-likeRs by 100 nM cocaine remained in the presence of GBR 12783. The observed cocaine-induced enhancement of the Gα_i/o-protein coupling of D₂Rs may be in part because of allosteric direct and/or indirect enhancing effects of cocaine at these receptors. These novel actions of cocaine may have relevance for understanding the actions of cocaine upon accumbal DA, and/or glutamate transmission and thus its rewarding as well as relapsing effects.     

Comparison of the Cardiac MicroPET Images Obtained Using [18F]FPTP and [13N]NH3 in Rat Myocardial Infarction Models

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A New Highly Deuterated [18F]AV-45, [18F]D15FSP,for Imaging β-Amyloid Plaques in the Brain

[¹⁸F]AV-45 (florbetapir f18, Amyvid) is an FDA-approved PET imaging agent targeting Aβ plaques in the brain for diagnosis of Alzheimer’s disease (AD). Its metabolites led to a high background in the brain and large bone uptake of [¹⁸F]F^–, produced from dealkylation of the PEG chain. To slow down the in vivo metabolism, we report the design, synthesis, and evaluation of a highly deuterated derivative, [¹⁸F]D15FSP, and compared it with N-methyl-deuterated [¹⁸F]D3FSP and nondeuterated [¹⁸F]AV-45. D15FSP displayed excellent binding affinity (K_i = 7.52 nM) to Aβ aggregates. In vitro autoradiography of [¹⁸F]D15FSP, [¹⁸F]D3FSP, and [¹⁸F]AV-45 showed excellent binding to Aβ plaques in human AD brain sections. Biodistribution studies displayed lower bone uptake at 120 min for [¹⁸F]D15FSP compared to that for [¹⁸F]D3FSP and [¹⁸F]AV-45 (1.44 vs 4.23 and 4.03%ID/g, respectively). As the highly deuterated [¹⁸F]D15FSP displayed excellent Aβ binding affinity, high initial brain penetration, and lower bone retention, it might be suitable for PET imaging in detecting Aβ plaques.     

Pharmacological comparison of UTP- and thapsigargin-induced arachidonic acid release in mouse RAW 264.7 macrophages

1. Although stimulation of mouse RAW 264.7 macrophages by UTP elicits a rapid increase in intracellular free Ca²⁺ ([Ca²⁺]_i), phosphoinositide (PI) turnover, and arachidonic acid (AA) release, the causal relationship between these signalling pathways is still unclear. In the present study, we investigated the involvement of phosphoinositide-dependent phospholipase C (PI-PLC) activation, Ca²⁺ increase and protein kinase activation in UTP-induced AA release. The effects of stimulating RAW 264.7 cells with thapsigargin, which cannot activate the inositol phosphate (IP) cascade, but results in the release of sequestered Ca²⁺ and an influx of extracellular Ca²⁺, was compared with the effects of UTP stimulation to elucidate the multiple regulatory pathways for cPLA₂ activation.
2. In RAW 264.7 cells UTP (100 μM) and thapsigargin (1  μM) caused 2 and 1.2 fold increases, respectively, in [³H]-AA release. The release of [³H]-AA following treatment with UTP and thapsigargin were non-additive, totally abolished in the Ca²⁺-free buffer, BAPTA (30 μM)-containing buffer or in the presence of the cPLA₂ inhibitor MAFP (50 μM), and inhibited by pretreatment of cells with pertussis toxin (100 ng ml⁻¹) or 4-bromophenacyl bromide (100 μM). By contrast, aristolochic acid (an inhibitor of sPLA₂) had no effect on UTP and thapsigargin responses.
3. {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075","term_text":"U73122"}}U73122 (10 μM) and neomycin (3 mM), inhibitors of PI-PLC, inhibited UTP-induced IP formation (88% and 83% inhibition, respectively) and AA release (76% and 58%, respectively), accompanied by a decrease in the [Ca²⁺]_i rise.
4. Wortmannin attenuated the IP response of UTP in a concentration-dependent manner (over the range 10 nM–3 μM), and reduced the UTP-induced AA release in parallel. RHC 80267 (30 μM), a specific diacylglycerol lipase inhibitor, had no effect on UTP-induced AA release.
5. Short-term treatment with PMA (1 μM) inhibited the UTP-stimulated accumulation of IP and increase in [Ca²⁺]_i, but had no effect on the release of AA. In contrast, the AA release caused by thapsigargin was increased by PMA.
6. The role of PKC in UTP- and thapsigargin-mediated AA release was shown by the blockade of these effects by staurosporine (1 μM), Ro 31-8220 (10 μM), Go 6976 (1 μM) and the down-regulation of PKC.
7. Following treatment of cells with SK&F 96365 (30 μM), thapsigargin-, but not UTP-, induced Ca²⁺ influx, and the accompanying AA release, were down-regulated.
8. Neither PD 98059 (100 μM), MEK a inhibitor, nor genistein (100 μM), a tyrosine kinase inhibitor, had any effect on the AA responses induced by UTP and thapsigargin.
9. We conclude that UTP-induced cPLA₂ activity depends on the activation of PI-PLC and the sustained elevation of intracellular Ca²⁺, which is essential for the activation of cPLA₂ by UTP and thapsigargin. The [Ca²⁺]_i-dependent AA release that follows treatment with both stimuli was potentiated by the activity of protein kinase C (PKC). A pertussis toxin-sensitive pathway downstream of the increase in [Ca²⁺]_i was also shown to be involved in AA release.

     

Phage display technology for stem cell delivery and systemic therapy

Advances in the technology for phage display in vivo have set the stage for a new ligand-directed pharmacology with broad implications for both treatment and molecular imaging of patients, and for the elucidation of molecular mechanisms of action, particularly in carcinogenesis. This technology identifies specific molecular complexes, mainly small peptide and gene-based therapeutic and imaging agents, effective in experimental animals and patients. The unbiased identification of molecular targets on the surfaces of blood vessels and parenchymal cells in preselected specific organs and tissues raises the prospect of an increased understanding of animal and human cellular and vascular proteomics. In this review, we focus on the delivery of phage-based agents via stem and progenitor cells, important delivery vehicles contributing to the growing impact of phage display on modern medicine.     

(−)‐[18F]Flubatine: evaluation in rhesus monkeys and a report of the first fully automated radiosynthesis validated for clinical use

(?)‐[¹⁸F]Flubatine was selected for clinical imaging of α₄β₂ nicotinic acetylcholine receptors because of its high affinity and appropriate kinetic profile. A fully automated synthesis of (?)‐[¹⁸F]flubatine as a sterile isotonic solution suitable for clinical use is reported, as well as the first evaluation in nonhuman primates (rhesus macaques). (?)‐[¹⁸F]Flubatine was prepared by fluorination of the Boc‐protected trimethylammonium iodide precursor with [¹⁸F]fluoride in an automated synthesis module. Subsequent deprotection of the Boc group with 1‐M HCl yielded (?)‐[¹⁸F]flubatine, which was purified by semi‐preparative HPLC. (?)‐[¹⁸F]Flubatine was prepared in 25% radiochemical yield (formulated for clinical use at end of synthesis, n = 3), >95% radiochemical purity, and specific activity = 4647 Ci/mmol (171.9 GBq/µmol). Doses met all quality control criteria confirming their suitability for clinical use. Evaluation of (?)‐[¹⁸F]flubatine in rhesus macaques was performed with a Concorde MicroPET P4 scanner (Concorde MicroSystems, Knoxville, TN). The brain was imaged for 90 min, and data were reconstructed using the 3‐D maximum a posteriori algorithm. Image analysis revealed higher uptake and slower washout in the thalamus than those in other areas of the brain and peak uptake at 45 min. Injection of 2.5 µg/kg of nifene at 60 min initiated a slow washout of [¹⁸F]flubatine, with about 25% clearance from the thalamus by the end of imaging at 90 min. Copyright © 2013 John Wiley & Sons, Ltd.     

A positron emission tomography (PET) study of cerebral dopamine D<Subscript>2</Subscript> and serotonine 5-HT<Subscript>2A</Subscript> receptor occupancy in patients treated with cyamemazine (Tercian)

Rationale Cyamemazine (Tercian) is an antipsychotic drug with anxiolytic properties. Recently, an in vitro study showed that cyamemazine possesses high affinity for serotonin 5-HT_2A receptors, which was fourfold higher than its affinity for dopamine D₂ receptors (Hameg et al. 2003).Objectives The aim of this study is to confirm these previous data in vivo in patients treated with clinically relevant doses of Tercian.Methods Eight patients received 37.5, 75, 150 or 300 mg/day of Tercian depending on their symptomatology. Dopamine D₂ and serotonin 5-HT_2A receptor occupancies (RO) were assessed at steady-state plasma levels of cyamemazine with positron emission tomography (PET), using [¹¹C]raclopride and [¹¹C]N-methyl-spiperone, respectively. The effective plasma level of the drug leading to 50% of receptor occupancy was estimated by fitting RO with plasma levels of cyamemazine at the time of the PET scan.Results Cyamemazine induced near saturation of 5-HT_2A receptors (RO=62.1–98.2%) in the frontal cortex even at low plasma levels of the drug. On the contrary, occupancy of striatal D₂ receptors increased with plasma levels, and no saturation was obtained even at high plasma levels (RO=25.2–74.9%). The effective plasma level of cyamemazine leading to 50% of D₂ receptor occupancy was fourfold higher than that for 5-HT_2A receptors. Accordingly, individual 5-HT_2A/D₂ RO ratios ranged from 1.26 to 2.68. No patients presented relevant increased prolactin levels, and only mild extrapyramidal side effects were noticed on Simpson and Angus Scale.Conclusion This in vivo binding study conducted in patients confirms previous in vitro findings indicating that cyamemazine has a higher affinity for serotonin 5-HT_2A receptors compared to dopamine D₂ receptors. In the dose range 37.5–300 mg, levels of dopamine D₂ occupancy remained below the level for motor side effects observed with typical antipsychotics and is likely to explain the low propensity of the drug to induce extrapyramidal side effects.     

Search for Compounds with Hypoglycemic Activity in the Series of 1-[2-(1H-Tetrazol-5-yl)-R1-phenyl]-3-R2-phenyl(ethyl)ureas and R1-Tetrazolo[1,5-c]quinazolin-5(6H)-ones

Methods of 1-[2-(1H-tetrazol-5-yl)-R¹-phenyl]-3-R²-phenyl(ethyl)ureas and R¹-tetrazolo[1,5-c]quinazolin-5(6H)-ones synthesis were designed. IR, LC-MS, ¹H NMR, and elemental analysis data evaluated the structure and purity of the obtained compounds. Different products, depending on the reaction conditions, were distinguished and discussed. The preliminary hypoglycemic activity of 36 synthesized compounds was revealed. Docking studies to 11β-hydroxysteroid dehydrogenase 1, γ-peroxisome proliferator-activated receptor, and dipeptidyl peptidase-4 were conducted. Eight of these substances were further tested on glucocorticoid-induced insulin resistance models, namely glucose tolerance, oral rapid insulin, and adrenalin tests. One of the most active compounds turned out to be tetrazolo[1,5-c]quinazolin-5(6H)-one 3.1, exceeding the reference drugs Metformin (50 and 200 mg/kg) and Gliclazide (50 mg/kg).