Spinocerebellar ataxia type 4 is caused by a GGC expansion in the ZFHX3 gene and is associated with prominent dysautonomia and motor neuron signs.

BACKGROUND: Spinocerebellar ataxia 4 (SCA4), characterized in 1996, features adult-onset ataxia, polyneuropathy, and linkage to chromosome 16q22.1; its underlying mutation has remained elusive. OBJECTIVE: To explore the radiological and neuropathological abnormalities in the entire neuroaxis in SCA4 and search for its mutation. METHODS: Three Swedish families with undiagnosed ataxia went through clinical, neurophysiological, and neuroimaging tests, including PET studies and genetic investigations. In four cases, neuropathological assessments of the neuroaxis were performed. Genetic testing included short read whole genome sequencing, short tandem repeat analysis with ExpansionHunter de novo, and long read sequencing. RESULTS: Novel features for SCA4 include dysautonomia, motor neuron affection, and abnormal eye movements. We found evidence of anticipation; neuroimaging demonstrated atrophy in the cerebellum, brainstem, and spinal cord. [18F]FDG-PET demonstrated brain hypometabolism and [11C]Flumazenil-PET reduced binding in several brain lobes, insula, thalamus, hypothalamus, and cerebellum. Moderate to severe loss of Purkinje cells in the cerebellum and of motor neurons in the anterior horns of the spinal cord along with pronounced degeneration of posterior tracts was also found. Intranuclear, mainly neuronal, inclusions positive for p62 and ubiquitin were sparse but widespread in the CNS. This finding prompted assessment for nucleotide expansions. A polyglycine stretch encoding GGC expansions in the last exon of the zink finger homeobox 3 gene was identified segregating with disease and not found in 1000 controls. CONCLUSIONS: SCA4 is a neurodegenerative disease caused by a novel GGC expansion in the coding region of ZFHX3, and its spectrum is expanded to include dysautonomia and neuromuscular manifestations.

Intraputamenal Cerebral Dopamine Neurotrophic Factor in Parkinson's Disease: A Randomized, Double-Blind, Multicenter Phase 1 Trial.

BACKGROUND: Cerebral dopamine neurotrophic factor (CDNF) is an unconventional neurotrophic factor that protects dopamine neurons and improves motor function in animal models of Parkinson's disease (PD). OBJECTIVE: The primary objectives of this study were to assess the safety and tolerability of both CDNF and the drug delivery system (DDS) in patients with PD of moderate severity. METHODS: We assessed the safety and tolerability of monthly intraputamenal CDNF infusions in patients with PD using an investigational DDS, a bone-anchored transcutaneous port connected to four catheters. This phase 1 trial was divided into a placebo-controlled, double-blind, 6-month main study followed by an active-treatment 6-month extension. Eligible patients, aged 35 to 75 years, had moderate idiopathic PD for 5 to 15 years and Hoehn and Yahr score ≤ 3 (off state). Seventeen patients were randomized to placebo (n = 6), 0.4 mg CDNF (n = 6), or 1.2 mg CDNF (n = 5). The primary endpoints were safety and tolerability of CDNF and DDS and catheter implantation accuracy. Secondary endpoints were measures of PD symptoms, including Unified Parkinson's Disease Rating Scale, and DDS patency and port stability. Exploratory endpoints included motor symptom assessment (PKG, Global Kinetics Pty Ltd, Melbourne, Australia) and positron emission tomography using dopamine transporter radioligand [18 F]FE-PE2I. RESULTS: Drug-related adverse events were mild to moderate with no difference between placebo and treatment groups. No severe adverse events were associated with the drug, and device delivery accuracy met specification. The severe adverse events recorded were associated with the infusion procedure and did not reoccur after procedural modification. There were no significant changes between placebo and CDNF treatment groups in secondary endpoints between baseline and the end of the main and extension studies. CONCLUSIONS: Intraputamenally administered CDNF was safe and well tolerated, and possible signs of biological response to the drug were observed in individual patients. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

[18F]FE-PE2I DAT correlates with Parkinson's disease duration, stage, and rigidity/bradykinesia scores: a PET radioligand validation study.

BACKGROUND: Correlations between dopamine transporter (DAT) availability and Parkinson's disease (PD) motor symptoms vary depending on the imaging modality, choice of regions of interest and clinical measures. We aimed to validate the PET radioligand [18F]FE-PE2I as a clinical biomarker in PD, hypothesizing negative correlations between DAT availability in specified nigrostriatal regions with symptom duration, disease stage and motor symptom scores. METHODS: We included 41 PD patients (age 45-79 years; H&Y stage < 3) and 37 healthy control subjects in a cross-sectional study with dynamic [18F]FE-PE2I PET. Binding potential (BPND) was estimated in the caudate nucleus, putamen, ventral striatum, sensorimotor striatum, and substantia nigra using the cerebellum as reference region. RESULTS: We found negative correlations (p < 0.02) between symptom duration and BPND in the putamen and sensorimotor striatum (rs = - .42; rs = - .51), and between H&Y stage and BPND in caudate nucleus, putamen, sensorimotor striatum, and substantia nigra (rs between - .40 and - .54). The first correlations were better described with exponential fitting. MDS-UPDRS-III in 'OFF' state correlated negatively (p < 0.04) with BPND in the sensorimotor striatum (rs = - .47), and excluding tremor score also in the putamen (rs = - .45). CONCLUSION: Results are in agreement with earlier findings in in vivo and post-mortem studies and validate [18F]FE-PE2I as a functional PD biomarker for PD severity. TRIAL REGISTRATION: EudraCT 2011-0020050, Registered April 26 2011; EudraCT 2017-003327-29, Registered October 08 2017; EudraCT 2017-001585-19, Registered August 2 2017. https://eudract.ema.europa.eu/ .

Striatal dopamine transporter and receptor availability correlate with relative cerebral blood flow measured with [11C]PE2I, [18F]FE-PE2I and [11C]raclopride PET in healthy individuals.

The aim of this retrospective study was to investigate relationships between relative cerebral blood flow and striatal dopamine transporter and dopamine D2/3 availability in healthy subjects. The data comprised dynamic PET scans with two dopamine transporter tracers [11C]PE2I (n = 20) and [18F]FE-PE2I (n = 20) and the D2/3 tracer [11C]raclopride (n = 18). Subjects with a [11C]PE2I scan also underwent a dynamic scan with the serotonin transporter tracer [11C]DASB. Binding potential (BPND) and relative tracer delivery (R1) values were calculated on regional and voxel-level. Striatal R1 and BPND values were correlated, using either an MRI-based volume of interest (VOI) or an isocontour VOI based on the parametric BPND image. An inter-tracer comparison between [11C]PE2I BPND and [11C]DASB R1 was done on a VOI-level and simulations were performed to investigate whether the constraints of the modeling could cause correlation of the parameters. A positive association was found between BPND and R1 for all three dopamine tracers. A similar correlation was found for the inter-tracer correlation between [11C]PE2I BPND and [11C]DASB R1. Simulations showed that this relationship was not caused by cross-correlation between parameters in the kinetic model. In conclusion, these results suggest an association between resting-state striatal dopamine function and relative blood flow in healthy subjects.

Quantification of the purinergic P2X7 receptor with [11C]SMW139 improves through correction for brain-penetrating radiometabolites.

The membrane-based purinergic 7 receptor (P2X7R) is expressed on activated microglia and the target of the radioligand [11C]SMW139 for in vivo assessment of neuroinflammation. This study investigated the contribution of radiolabelled metabolites which potentially affect its quantification. Ex vivo high-performance liquid chromatography with a radio detector (radioHPLC) was used to evaluate the parent and radiometabolite fractions of [11C]SMW139 in the brain and plasma of eleven mice. Twelve healthy humans underwent 90-min [11C]SMW139 brain PET with arterial blood sampling and radiometabolite analysis. The volume of distribution was estimated by using one- and two- tissue compartment (TCM) modeling with single (VT) and dual (VTp) input functions. RadioHPLC showed three major groups of radiometabolite peaks with increasing concentrations in the plasma of all mice and humans. Two radiometabolite peaks were also visible in mice brain homogenates and therefore considered for dual input modeling in humans. 2TCM with single input function provided VT estimates with a wide range (0.10-10.74) and high coefficient of variation (COV: 159.9%), whereas dual input function model showed a narrow range of VTp estimates (0.04-0.24; COV: 33.3%). In conclusion, compartment modeling with correction for brain-penetrant radiometabolites improves the in vivo quantification of [11C]SMW139 binding to P2X7R in the human brain.

Development of Parkinsonism in a Patient with Central Pontine Myelinolysis.

Osmotic demyelination syndrome (ODS) is caused by damage to the pons myelin sheath and nerve cells. Although the pathophysiological mechanism responsible for the damage is not yet fully understood, it is currently believed that osmotic-type changes (especially if they are massive and too rapid) cause oedema that leads to compression and, subsequently, demyelination of white matter fibres. It generally manifests with acute paraparesis/tetraparesis, dysphagia, dysarthria, diplopia, and loss of consciousness, as well as hallucinations, spasms, and other neurological symptoms related to brainstem damage. In extreme cases, the locked-in syndrome may also appear. Of note, in some cases an association between osmotic demyelinating damage and the onset of movement disorders has been documented and, although the pathophysiology is still unknown, a correlation has been postulated between ODS and movement disorders. Here, we present a patient with ODS who developed parkinsonism, thus supporting the hypothesis of a correlation between these pathological events.

Simplified quantification of [18F]FE-PE2I PET in Parkinson's disease: Discriminative power, test-retest reliability and longitudinal validity during early peak and late pseudo-equilibrium.

Quantification of dopamine transporter (DAT) availability with [18F]FE-PE2I PET enables the detection of presynaptic dopamine deficiency and provides a potential progression marker for Parkinson`s disease (PD). Simplified quantification is feasible, but the time window of short acquisition protocols may have a substantial impact on the reliability of striatal binding estimates. Dynamic [18F]FE-PE2I PET data of cross-sectional (33 PD patients, 24 controls), test-retest (9 patients), and longitudinal (12 patients) cohorts were used to assess the variability and reliability of specific binding ratios (SBR) measured during early peak and late pseudo-equilibrium. Receiver operating characteristics area under the curve (PD vs. controls) was high for early (0.996) and late (0.991) SBR. Early SBR provided more favourable effect size, absolute variability, and standard error of measurement than late SBR (caudate: 1.29 vs. 1.23; 6.9% vs. 9.8%; 0.09 vs. 0.20; putamen: 1.75 vs. 1.67; 7.7% vs. 14.0%; 0.08 vs. 0.17). The annual percentage change was comparable for both time windows (-7.2%-8.5%), but decline was significant only for early SBR. Whereas early and late [18F]FE-PE2I PET acquisitions have similar discriminative power to separate PD patients and controls, the early peak equilibrium acquisition can be recommended if [18F]FE-PE2I is used to measure longitudinal changes of DAT availability.

Reliability of dopamine transporter PET measurements with [18F]FE-PE2I in patients with Parkinson's disease.

BACKGROUND: Reliable quantification of dopamine transporter (DAT), a biomarker for Parkinson's disease (PD), is essential for diagnostic purposes as well as for evaluation of potential disease-modifying treatment. Due to degeneration of dopaminergic neurons and thus lower expected radioligand binding to DAT, higher measurement variability in PD patients might be expected than earlier reproducibility results in healthy controls. Therefore, we aimed to examine the test-retest properties of [18F]FE-PE2I-PET in PD patients. METHODS: Nine patients with PD (Hoehn and Yahr stage < 3) were included (men/women 6/3; mean age 65.2 ± 6.8 years). Each patient underwent two [18F]FE-PE2I-PET measurements within 7-28 days. The outcome measure was non-displaceable binding potential generated using wavelet-aided parametric imaging with cerebellum as reference region. We assessed test-retest performance using estimates of reliability and repeatability. Regions for primary analysis were caudate, putamen, ventral striatum, and substantia nigra. Exploratory analysis was performed for functional subdivisions of the striatum. We also compared the more vs. less affected side. RESULTS: [18F]FE-PE2I showed absolute variability estimates of 5.3-7.6% in striatal regions and 11% in substantia nigra and ICCs of 0.74-0.97 (median 0.91). The absolute variability for functional striatal subdivisions was 6.0-9.6% and ICCs of 0.76-0.91 (median 0.91). The less affected substantia nigra exhibited greater consistency than the more affected side. According to power calculations based on the current sample size, DAT changes of 5-11% in the striatum and 28% in the substantia nigra can be detected with a power of 0.8 (p < 0.0125). CONCLUSION: DAT-PET measurements with [18F]FE-PE2I in PD patients showed good repeatability and reliability. The slightly lower reliability in the substantia nigra in patients may be explained by lower DAT density and smaller anatomical size. Power calculations suggest that [18F]FE-PE2I PET is a suitable marker for longitudinal DAT decline in PD. TRIAL REGISTRATION: EudraCT 2017-003327-29.

High-resolution PET imaging reveals subtle impairment of the serotonin transporter in an early non-depressed Parkinson's disease cohort.

PURPOSE: The serotonin transporter (SERT) is a biochemical marker for monoaminergic signaling in brain and has been suggested to be involved inthe pathophysiology of Parkinson's disease (PD). The aim of this PET study was to examine SERT availability in relevant brain regions in early stages ofnon-depressed PD patients. METHODS: In a cross-sectional study, 18 PD patients (13 M/5F, 64 ± 7 years, range 46-74 years, disease duration 2.9 ± 2.6 years; UPDRS motor 21.9 ± 5.2) and 20 age- and gender-matched healthy control (HC) subjects (15 M/5F, 61 ± 7 years, range 50-72 years) were included. In a subsequent longitudinal phase, ten of the PD patients (7 M/3F, UPDRS motor 20.6 ± 6.9) underwent a second PET measurement after 18-24 months. After a 3-T MRI acquisition, baseline PET measurements were performed with [11C]MADAM using a high-resolution research tomograph. The non-displaceablebinding potential (BPND) was chosen as the outcome measure and was estimated at voxel level on wavelet-aided parametric images, by using the Logan graphical analysis and the cerebellum as reference region. A molecular template was generated to visualize and define different subdivisions of the raphe nuclei in the brainstem. Subortical and cortical regions of interest were segmented using FreeSurfer. Univariate analyses and multivariate network analyses were performed on the PET data. RESULTS: The univariate region-based analysis showed no differences in SERT levels when the PD patients were compared with the HC neither at baseline or after 2 years of follow-up. The multivariate network analysis also showed no differences at baseline. However, prominent changes in integration and segregation measures were observed at follow-up, indicating a disconnection of the cortical and subcortical regions from the three nuclei of the raphe. CONCLUSION: We conclude that the serotoninergic system in PD patients seems to become involved with a network dysregulation as the disease progresses, suggesting a disturbed serotonergic signaling from raphe nuclei to target subcortical and cortical regions.

PET Molecular Imaging of Phosphodiesterase 10A: An Early Biomarker of Huntington's Disease Progression.

BACKGROUND: Changes in phosphodiesterase 10A enzyme levels may be a suitable biomarker of disease progression in Huntington's disease. OBJECTIVES: To evaluate phosphodiesterase 10A PET imaging as a biomarker of HD progression using the radioligand, [18 F]MNI-659. METHODS: The cross-sectional study (NCT02061722) included 45 Huntington's disease gene-expansion carriers stratified into four disease stages (early and late premanifest and Huntington's disease stages 1 and 2) and 45 age- and sex-matched healthy controls. The primary analysis compared striatal and pallidal phosphodiesterase 10A availability between Huntington's disease gene-expansion carriers and healthy controls as assessed by [18 F]MNI-659 binding. We assessed changes in phosphodiesterase 10A expression using several PET methodologies and compared with previously proposed measures of Huntington's disease progression (PET imaging of D2/3 receptors and anatomical volume loss on MRI). The longitudinal follow-up study (NCT02956148) continued evaluation of phosphodiesterase 10A availability in 35 Huntington's disease gene-expansion carriers at a mean of 18 months from baseline of the cross-sectional study. RESULTS: Primary analyses revealed that phosphodiesterase 10A availability in caudate, putamen, and globus pallidus was significantly lower in Huntington's disease gene-expansion carriers versus healthy controls across all stages. Striatal and pallidal phosphodiesterase 10A availability progressively declined in the premanifest stages and appeared to plateau between stages 1 and 2. The percentage decline of phosphodiesterase 10A availability measured cross-sectionally between Huntington's disease gene-expansion carriers and healthy controls was greater than that demonstrated by D2/3 receptor availability or volumetric changes. Annualized rates of phosphodiesterase 10A change showed a statistically significant decline between the cross-sectional study and follow-up. CONCLUSIONS: [18 F]MNI-659 PET imaging is a biologically plausible biomarker of Huntington's disease progression that is more sensitive than the dopamine-receptor and volumetric methods currently used. © 2020 International Parkinson and Movement Disorder Society.

Novel Imaging Biomarkers for Huntington's Disease and Other Hereditary Choreas.

PURPOSE OF THE REVIEW: Imaging biomarkers for neurodegenerative disorders are primarily developed with the goal to aid diagnosis, to monitor disease progression, and to assess the efficacy of disease-modifying therapies in support to clinical outcomes that may either show limited sensitivity or need extended time for their evaluation. This article will review the most recent concepts and findings in the field of neuroimaging applied to Huntington's disease and Huntington-like syndromes. Emphasis will be given to the discussion of potential pharmacodynamic biomarkers for clinical trials in Huntington's disease (HD) and of neuroimaging tools that can be used as diagnostic biomarkers in HD-like syndromes. RECENT FINDINGS: Several magnetic resonance (MR) and positron emission tomography (PET) molecular imaging tools have been identified as potential pharmacodynamic biomarkers and others are in the pipeline after preclinical validation. MRI and 18F-fluorodeoxyglucose PET can be considered useful supportive diagnostic tools for the differentiation of other HD-like syndromes. New trials in HD have the primary goal to lower mutant huntingtin (mHTT) protein levels in the brain in order to reduce or alter the progression of the disease. MR and PET molecular imaging markers have been developed as tools to monitor disease progression and to evaluate treatment outcomes of disease-modifying trials in HD. These markers could be used alone or in combination for detecting structural and pharmacodynamic changes potentially associated with the lowering of mHTT.

Nigrostriatal dopamine transporter availability in early Parkinson's disease.

BACKGROUND: The imaging of biomarkers for characterization of dopaminergic impairment in Parkinson's disease (PD) is useful for diagnosis, patient stratification, and assessment of treatment outcomes. [18 F]FE-PE2I is an improved imaging tool allowing for detailed mapping of the dopamine transporter protein in the nigro-striatal system at the level of cell bodies (substantia nigra), axons, and presynaptic terminals (striatum). OBJECTIVES: The objective of this study was to compare the dopamine transporter protein loss in the presynaptic terminals to that in the cell bodies and axons in early PD patients using [18 F](E)-N-(3-iodoprop-2-enyl)-2b-carbofluoroethoxy-3b-(4'-methyl-phenyl) nortropane ([18 F]FE-PE2I) and high-resolution PET. METHODS: A total of 20 early PD patients (15 men/5 women, 62 ± 8 years) and 20 controls (15 men/5 women, 62 ± 7 years) underwent high-resolution [18 F]FE-PE2I PET. Dopamine transporter protein availability was estimated for the different nigro-striatal regions and expressed as nondisplaceable binding potential values. RESULTS: When compared with controls, the binding potential values in PD patients were reduced by 36% to 70% in presynaptic terminals and by 30% in cell bodies. Dopamine transporter availability along the tracts was not different between the 2 groups (controls 0.5 ± 0.1 vs PD 0.4 ± 0.1). CONCLUSIONS: This is the first study that examines dopamine transporter protein availability in vivo within the entire nigro-striatal pathway. The results suggest that at early stages of symptomatic PD a greater loss is observed at the level of the axonal terminals when compared with cell bodies and axons of dopaminergic neurons. The findings suggest a relative preservation of cell bodies in early PD, which might be relevant for novel disease-modifying strategies. © 2018 International Parkinson and Movement Disorder Society.

Revisiting the Logan plot to account for non-negligible blood volume in brain tissue.

BACKGROUND: Reference tissue-based quantification of brain PET data does not typically include correction for signal originating from blood vessels, which is known to result in biased outcome measures. The bias extent depends on the amount of radioactivity in the blood vessels. In this study, we seek to revisit the well-established Logan plot and derive alternative formulations that provide estimation of distribution volume ratios (DVRs) that are corrected for the signal originating from the vasculature. RESULTS: New expressions for the Logan plot based on arterial input function and reference tissue were derived, which included explicit terms for whole blood radioactivity. The new methods were evaluated using PET data acquired using [11C]raclopride and [18F]MNI-659. The two-tissue compartment model (2TCM), with which signal originating from blood can be explicitly modeled, was used as a gold standard. DVR values obtained for [11C]raclopride using the either blood-based or reference tissue-based Logan plot were systematically underestimated compared to 2TCM, and for [18F]MNI-659, a proportionality bias was observed, i.e., the bias varied across regions. The biases disappeared when optimal blood-signal correction was used for respective tracer, although for the case of [18F]MNI-659 a small but systematic overestimation of DVR was still observed. CONCLUSIONS: The new method appears to remove the bias introduced due to absence of correction for blood volume in regular graphical analysis and can be considered in clinical studies. Further studies are however required to derive a generic mapping between plasma and whole-blood radioactivity levels.

Patterns of age related changes for phosphodiesterase type-10A in comparison with dopamine D2/3 receptors and sub-cortical volumes in the human basal ganglia: A PET study with 18F-MNI-659 and 11C-raclopride with correction for partial volume effect.

Phosphodiesterase 10A enzyme (PDE10A) is an important striatal target that has been shown to be affected in patients with neurodegenerative disorders, particularly Huntington´s disease (HD). PDE10A is expressed on striatal neurones in basal ganglia where other known molecular targets are enriched such as dopamine D2/3 receptors (D2/3 R). The aim of this study was to examine the availability of PDE10A enzyme in relation with age and gender and to compare those changes with those related to D2/3 R and volumes in different regions of the basal ganglia. As a secondary objective we examined the relative distribution of D2/3 R and PDE10A enzyme in the striatum and globus pallidus. Forty control subjects (20F/20M; age: 44±11y, age range 27-69) from an ongoing positron emission tomography (PET) study in HD gene expansion carriers were included. Subjects were examined with PET using the high-resolution research tomograph (HRRT) and with 3T magnetic resonance imaging (MRI). The PDE10A radioligand 18F-MNI-659 and D2/3 R radioligand 11C-raclopride were used. The outcome measure was the binding potential (BPND) estimated with the two-tissue compartment model (18F-MNI-659) and the simplified reference tissue model (11C-raclopride) using the cerebellum as reference region. The PET data were corrected for partial volume effects. In the striatum, PDE10A availability showed a significant age-related decline that was larger compared to the age-related decline of D2/3 R availability and to the age-related decline of volumes measured with MRI. In the globus pallidus, a less pronounced decline of PDE10A availability was observed, whereas D2/3 R availability and volumes seemed to be rather stable with aging. The distribution of the PDE10A enzyme was different from the distribution of D2/3 R, with higher availability in the globus pallidus. These results indicate that aging is associated with a considerable physiological reduction of the availability of PDE10A enzyme in the striatum. Moreover as result of the analysis, in the striatum for both the molecular targets, we observed a gender effect with higher BPND the female group.

In vivo measurement of PDE10A enzyme occupancy by positron emission tomography (PET) following single oral dose administration of PF-02545920 in healthy male subjects.

Phosphodiesterase 10A (PDE10A) is an enzyme highly enriched in the striatal medium spiny neurons. It is involved in the regulation of cytoplasmic levels of cAMP and cGMP and signaling within the basal ganglia. This study with PDE10A radioligand [18F]MNI-659 was designed to measure the enzyme occupancy of PF-02545920 in 8 healthy male volunteers (48 ± 4 years) after a single oral dose (10 mg or 20 mg) and to evaluate safety and tolerability. Arterial blood sampling was performed to obtain a metabolite-corrected plasma input function for the quantification of [18F]MNI-659 binding to PDE10A. The occupancy of PF-02545920 was calculated with two different methods: In Method 1, [18F]MNI-659 enzyme occupancy was calculated from the estimates of binding potential, using the cerebellum as a reference region; in Method 2, occupancy was estimated from the slope of the revised Lassen's plot. Serum concentrations of PF-02545920 were measured to determine the relationship between concentration and occupancy. Based on Method 1, striatal PDE10A occupancy increased with increasing PF-02545920 dose: 14-27% at 10 mg dose (N = 4) and 45-63% at 20 mg dose (N = 3). Comparable occupancies were observed using Lassen's plot Method 2: 10 mg: 14-37%; 20 mg: 46-55%. The relationship between exposure and occupancy was best described using an Emax model. The serum concentration associated with 50% occupancy was estimated to be 93.2 ng/mL. Single oral doses of 10 mg or 20 mg of PF-02545920 were safe and well tolerated in healthy male volunteers [NCT# 01918202].

Positron emission tomography measurement of brain MAO-B inhibition in patients with Alzheimer's disease and elderly controls after oral administration of sembragiline.

PURPOSE: In Alzheimer's disease (AD), increased metabolism of monoamines by monoamine oxidase type B (MAO-B) leads to the production of toxic reactive oxygen species (ROS), which are thought to contribute to disease pathogenesis. Inhibition of the MAO-B enzyme may restore brain levels of monoaminergic neurotransmitters, reduce the formation of toxic ROS and reduce neuroinflammation (reactive astrocytosis), potentially leading to neuroprotection. Sembragiline (also referred as RO4602522, RG1577 and EVT 302 in previous communications) is a potent, selective and reversible inhibitor of MAO-B developed as a potential treatment for AD. METHODS: This study assessed the relationship between plasma concentration of sembragiline and brain MAO-B inhibition in patients with AD and in healthy elderly control (EC) subjects. Positron emission tomography (PET) scans using [11C]-L-deprenyl-D2 radiotracer were performed in ten patients with AD and six EC subjects, who received sembragiline each day for 6-15 days. RESULTS: At steady state, the relationship between sembragiline plasma concentration and MAO-B inhibition resulted in an Emax of ∼80-90 % across brain regions of interest and in an EC50 of 1-2 ng/mL. Data in patients with AD and EC subjects showed that near-maximal inhibition of brain MAO-B was achieved with 1 mg sembragiline daily, regardless of the population, whereas lower doses resulted in lower and variable brain MAO-B inhibition. CONCLUSIONS: This PET study confirmed that daily treatment of at least 1 mg sembragiline resulted in near-maximal inhibition of brain MAO-B enzyme in patients with AD.

Optimal Acquisition Time Window and Simplified Quantification of Dopamine Transporter Availability Using 18F-FE-PE2I in Healthy Controls and Parkinson Disease Patients.

18F-(E)-N-(3-iodoprop-2-enyl)-2ß-carbofluoroethoxy-3ß-(4'methylphenyl)nortropane (18F-FE-PE2I) is a newly developed dopamine transporter (DAT) PET radioligand. Full quantification methods rely on dynamic acquisition of 18F-FE-PE2I, but in a clinical setting a simplified protocol is preferable. The aims of this study were to identify the optimal acquisition time window for 18F-FE-PE2I and to validate the specific binding ratio (SBR) as a simplified quantification method. METHODS: Ten Parkinson disease (PD) patients and 10 controls were included. Ninety-three-min dynamic PET measurements with 18F-FE-PE2I were conducted using the high-resolution research tomograph (HRRT). The dynamic measurement was also smoothed to the resolution of a clinical PET system (HR). Regions of interest for the caudate, putamen, ventral striatum, substantia nigra (SN), and cerebellum were manually drawn on coregistered MR images. The outcome measure was the SBR, and the gold standard was the binding potential obtained with wavelet-aided parametric imaging (WAPI BPND). The cerebellum was used as a reference region. In a preliminary analysis, SBR was computed for 8 time windows (SBRdyn). Linear regression analysis and Bland-Altman plots were used to select the optimal acquisition time window. An average image from the selected time window was created, from which new SBR values (SBR calculated on the average image on the HRRT and SBR calculated on the average image on the simulated HR images) were calculated and compared with WAPI BPND The effect size was calculated. RESULTS: SBRdyn values for the time window between 16.5 and 42 min correlated best with WAPI BPND (r2 = 0.98, P < 0.001). Significant correlations (P < 0.001) were observed between SBRHR and WAPI-BPND (r2 = 0.95 in controls and 0.97 in PD patients). In the striatum, SBRHR values were 37% lower than BPND in controls, 29% in PD patients, whereas in the SN the underestimation was 22% in controls and 15% in PD patients. Similar effect sizes for BPND and SBRHR were found in the caudate (0.6), putamen (1.7 and 1.4), ventral striatum (0.7), and SN (0.5 and 0.4). CONCLUSION: A single 18F-FE-PE2I acquisition between 16.5 and 42 min provides the best outcome measure for simplified DAT quantification. Despite underestimation of the BPND, the SBR can be used in a clinical setting as a valid quantification method for DAT using 18F-FE-PE2I, because it provides differentiation similar to BPND between controls and PD patients.

In Vivo and In Vitro Characterization of a Novel MAO-B Inhibitor Radioligand, 18F-Labeled Deuterated Fluorodeprenyl.

UNLABELLED: The aim of this study was to radiolabel a novel bis-deuterium substituted l-deprenyl analog (fluorodeprenyl-D2) with (18)F and to evaluate its potential to visualize and quantify monoamine oxidase (MAO) B activity in vivo. METHODS: The precursor compound ( 5A: + 5B: ) and reference standard ( 6: ) were synthesized in multistep syntheses. Recombinant human MAO-B and MAO-A enzyme preparations were used to determine inhibitory concentrations of 50%. Radiolabeling was accomplished by a nucleophilic substitution reaction. Whole-hemisphere autoradiography was performed with (18)F-fluorodeprenyl-D2. A PET study was performed on a cynomolgus monkey. Radiometabolites were measured in monkey plasma using high-performance liquid chromatography. RESULTS: The 50% inhibitory concentration of compound 6 for MAO-B was 227 ± 36.8 nM. Radiolabeling was accomplished with high radiochemical yield, purity, and specific radioactivity. The autoradiography binding density of (18)F-fluorodeprenyl-D2 was consistent with known MAO-B expression in the human brain. In vivo, (18)F-fluorodeprenyl-D2 showed favorable kinetic properties, with relatively fast washout from the brain. Regional time-activity curves were better described by the 2-tissue-compartment model. Administration of a 1 mg/kg dose of l-deprenyl yielded 70% inhibition of MAO-B in all regions. Radiometabolite studies demonstrated 20% unchanged radioligand at 120 min after injection. (18)F-fluorodeprenyl-D2 showed less irreversibility than did previously reported MAO-B radioligands. CONCLUSION: The results suggest that (18)F-fluorodeprenyl-D2 is a suitable PET radioligand for visualization of MAO-B activity in the human brain.

Quantitative Analysis of ¹8F-(E)-N-(3-Iodoprop-2-Enyl)-2ß-Carbofluoroethoxy-3ß-(4'-Methyl-Phenyl) Nortropane Binding to the Dopamine Transporter in Parkinson Disease.

UNLABELLED: (18)F-(E)-N-(3-iodoprop-2-enyl)-2ß-carbofluoroethoxy-3ß-(4'-methyl-phenyl) nortropane ((18)F-FE-PE2I) is a recently developed radioligand for the in vivo quantification of the dopamine transporter (DAT) in the striatum and substantia nigra (SN). The aim of this study was to examine the suitability of (18)F-FE-PE2I as a tool for imaging the nigrostriatal pathway in Parkinson disease (PD) with PET. METHODS: Ten PD patients (9 men and 1 woman; mean age ± SD, 60 ± 9 y; Hoehn and Yahr, 1-2; Unified Parkinson Disease Rating Scale motor, 18.9 ± 6.7) and 10 controls (9 men and 1 woman; mean age ± SD, 60 ± 7 y) were included. PET measurements with (18)F-FE-PE2I were conducted for 93 min using the High-Resolution Research Tomograph. Venous blood was drawn to compare protein binding, parent fraction, and radiometabolite composition in PD patients and controls. Regions of interest for the caudate, putamen, ventral striatum, SN, and cerebellum were drawn on coregistered MR images. The outcome measure was the binding potential (BP(ND)) estimated with the simplified reference tissue model and the Logan graphical analysis, using the cerebellum as a reference region. Time stability of BP(ND) was examined to define the shortest acquisition protocol for quantitative studies. The wavelet-aided parametric imaging method was used to obtain high-resolution BP(ND) images to compare DAT availability in the striatum and SN in PD patients and control subjects. Group differences were assessed with the unpaired t test (P < 0.05). RESULTS: Parent, radiometabolite fractions, plasma concentration, and cerebellar uptake of (18)F-FE-PE2I did not differ significantly between PD patients and controls. Stable estimates of BP(ND) (<8% of the 93-min value) were obtained with the simplified reference tissue model using approximately 66 min of data. BP(ND) values in PD patients were significantly lower than those in controls (P < 0.05) in the caudate (2.54 ± 0.79 vs. 3.68 ± 0.56), putamen (1.39 ± 1.04 vs. 4.41 ± 0.54), ventral striatum (2.26 ± 0.93 vs. 3.30 ± 0.46), and SN (0.46 ± 0.20 vs. 0.68 ± 0.15). CONCLUSION: (18)F-FE-PE2I is clearly a suitable radioligand for DAT quantification and imaging of the nigrostriatal pathway in PD. Similar metabolism in controls and PD patients, suitability of the cerebellum as a reference region, and accuracy of quantification using approximately 66 min of PET data are advantages for noninvasive and simplified imaging protocols for PD studies. Finally, DAT loss in PD can be measured in both the striatum and the SN, supporting the utility of (18)F-FE-PE2I as an imaging tool of the nigrostriatal pathway.

Altered resting state effective connectivity in long-standing vegetative state patients: an EEG study.

OBJECTIVE: Recent evidence mainly based on hemodynamic measures suggests that the impairment of functional connections between different brain areas may help to clarify the neuronal dysfunction occurring in patients with disorders of consciousness (DOC). The aim of this study was to evaluate effective EEG connectivity in a cohort of 18 patients in a chronic vegetative state (VS) observed years after the occurrence of hypoxic (eight) and traumatic or hemorrhagic brain insult. METHODS: we analysed the EEG signals recorded under resting conditions using a frequency domain linear index of connectivity (partial directed coherence: PDC) estimated from a multivariate autoregressive model. The results were compared with those obtained in ten healthy controls. RESULTS: Our findings indicated significant connectivity changes in EEG activities in delta and alpha bands. The VS patients showed a significant and widespread decrease in delta band connectivity, whereas the alpha activity was hyper-connected in the central and posterior cortical regions. CONCLUSION: These changes suggest the occurrence of severe circuitry derangements probably due to the loose control of the subcortical connections. The alpha hyper-synchronisation may be due to simplified networks mainly involving the short-range connections between intrinsically oscillatory cortical neurons that generate aberrant EEG alpha sources. This increased connectivity may be interpreted as a reduction in information capacity, implying an increasing prevalence of stereotypic activity patterns. SIGNIFICANCE: Our observations suggest a remarkable rearrangement of connectivity in patients with long-standing VS. We hypothesize that in persistent VS, after a first period characterized by a breakdown of cortical connectivity, neurodegenerative processes, largely independent from the type of initial insult, lead to cortex de-afferentation and to a severe reduction of possible cortical activity patterns and states.