Publications by authors named "Päivi Marjamäki"

39 Publications

Association of Early β-Amyloid Accumulation and Neuroinflammation Measured With [C]PBR28 in Elderly Individuals Without Dementia.

Neurology 2021 Mar 29;96(12):e1608-e1619. Epub 2021 Jan 29.

From the Turku PET Centre (S.T., L.L.E., J.T., S.H., J.J., P.M., J.O.R.) and Department of Biostatistics (E.L.), University of Turku; Kuopio City Home Care (S.T.), Rehabilitation and Medical Services for Elderly, Kuopio, Finland; Amsterdam Alzheimer Center (L.L.E.), Amsterdam UMC, the Netherlands; Department of Radiation Sciences (J.J.), Umeå University, Sweden; City of Turku (H.L.), Welfare Division, Turku City Hospital, Turku, Finland; Department of Medicine (H.L.), University of Turku, Turku University Hospital, Finland; Department of Psychiatry and Neurochemistry (K.B., H.Z.), Institute of Neuroscience and Physiology, the Sahlgrenska Academy at the University of Gothenburg; Clinical Neurochemistry Laboratory (K.B., H.Z.), Sahlgrenska University Hospital, Mölndal, Sweden; Department of Neurodegenerative Disease (H.Z.), UCL Institute of Neurology, Queen Square; UK Dementia Research Institute at UCL (H.Z.), London; National Institute for Health and Welfare (A.J.); Department of Geriatrics (M.V.), Turku City Hospital; University of Turku (M.V.), Finland; Division of Clinical Geriatrics (M.V.), NVS, Karolinska Institutet, Stockholm, Sweden; and Division of Clinical Neurosciences (J.O.R.), Turku University Hospital, Finland.

Objective: To examine whether early β-amyloid (Aβ) accumulation and metabolic risk factors are associated with neuroinflammation in elderly individuals without dementia.

Methods: We examined 54 volunteers (mean age 70.0 years, 56% women, 51% ɛ4 carriers) with the translocator protein (TSPO) tracer [C]PBR28 to assess neuroinflammation and with [C] Pittsburgh compound B (PiB) to assess cerebral Aβ accumulation. [C]PBR28 and [C]PiB standardized uptake value ratios (SUVRs) were quantified in 6 regions of interests by using the cerebellar cortex as a pseudo-reference and reference region, respectively. Fasting venous glucose, insulin, and high-sensitivity C-reactive protein (hs-CRP) values were determined. Homeostatic model assessment of insulin resistance (HOMA-IR) was calculated. A subset of individuals (n = 11) underwent CSF sampling, and Aβ, Aβ, total tau, phospho-tau, soluble TREM2, and YKL-40 levels were measured.

Results: Among the whole study group, no significant association was found between [C]PiB and [C]PBR28 SUVR composite scores (slope 0.02, = 0.30). However, higher [C]PiB binding was associated with higher [C]PBR28 binding among amyloid-negative ([C]PiB composite score ≤1.5) (TSPO genotype-, age- and sex-adjusted slope 0.26, = 0.008) but not among amyloid-positive (slope -0.004, = 0.88) participants. Higher CSF soluble TREM2 ( = 0.72, = 0.01) and YKL-40 ( = 0.63, = 0.04) concentrations were associated with a higher [C]PBR28 composite score. Higher body mass index, HOMA-IR, and hs-CRP were associated with higher [C]PBR28 binding in brain regions where Aβ accumulation is first detected in Alzheimer disease.

Conclusions: While there was no association between amyloid and neuroinflammation in the overall study group, neuroinflammation was associated with amyloid among the subgroup at early stages of amyloid pathology.
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http://dx.doi.org/10.1212/WNL.0000000000011612DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8032368PMC
March 2021

Application of the PET ligand [C]ORM-13070 to examine receptor occupancy by the α-adrenoceptor antagonist ORM-12741: translational validation of target engagement in rat and human brain.

EJNMMI Res 2020 Dec 9;10(1):152. Epub 2020 Dec 9.

Orion Corporation, Orion Pharma, Research and Development, Tengströminkatu 8, 20380, Espoo, Finland.

Background: Availability of the α-adrenoceptor (α-AR) positron emission tomography (PET) tracer, [C]ORM-13070, and the α-AR antagonist ORM-12741 allows probing of the roles of this G-protein coupled receptor subtype in brain function, both in healthy humans and in patients with various brain disorders. This translational study employed [C]ORM-13070 autoradiography and PET to determine α-AR occupancy by ORM-12741 in rat and human brain, respectively.

Results: ORM-12741 has high affinity (K: 0.08 nM) and potent antagonist activity (K: 0.04 nM) as well as selectivity (K estimates for the human α-AR and α-AR were 8.3 nM and 0.8 nM, respectively) for the human α-AR subtype. [C]ORM-13070 had highest uptake in the basal ganglia of rat and human brain. Pretreatment with ORM-12741 inhibited [C]ORM-13070 binding in rat striatum in a time- and dose-dependent manner at 10 and 50 µg/kg (s.c.) with an EC estimate of 1.42 ng/mL in rat plasma, corresponding to protein-free drug concentration of 0.23 nM. In the living human brain, time- and dose-related α-AR occupancy was detected with EC estimates of 24 ng/mL and 31 ng/mL for the caudate nucleus and putamen, respectively, corresponding to protein-free concentrations in plasma of 0.07 nM and 0.1 nM. Modelling-based maximum α-AR occupancy estimates were 63% and 52% in the caudate nucleus and the putamen, respectively.

Conclusions: ORM-12741 is a selective α-AR antagonist which penetrates the rat and human brain to occupy α-ARs in a manner consistent with its receptor pharmacology. Trial registration number and date of registration: ClinicalTrial.cov NCT00829907. Registered 11 December 2008. https://clinicaltrials.gov/ .
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http://dx.doi.org/10.1186/s13550-020-00741-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7726058PMC
December 2020

The circadian gene Cryptochrome 2 influences stress-induced brain activity and depressive-like behavior in mice.

Genes Brain Behav 2021 Apr 26;20(4):e12708. Epub 2020 Oct 26.

Molecular and Integrative Biosciences Research Program, University of Helsinki, Helsinki, Finland.

Cryptochrome 2 (Cry2) is a core clock gene important for circadian regulation. It has also been associated with anxiety and depressive-like behaviors in mice, but the previous findings have been conflicting in terms of the direction of the effect. To begin to elucidate the molecular mechanisms of this association, we carried out behavioral testing, PET imaging, and gene expression analysis of Cry2 and Cry2 mice. Compared to Cry2 mice, we found that Cry2 mice spent less time immobile in the forced swim test, suggesting reduced despair-like behavior. Moreover, Cry2 mice had lower saccharin preference, indicative of increased anhedonia. In contrast, we observed no group differences in anxiety-like behavior. The behavioral changes were accompanied by lower metabolic activity of the ventro-medial hypothalamus, suprachiasmatic nuclei, ventral tegmental area, anterior and medial striatum, substantia nigra, and habenula after cold stress as measured by PET imaging with a glucose analog. Although the expression of many depression-associated and metabolic genes was upregulated or downregulated by cold stress, we observed no differences between Cry2 and Cry2 mice. These findings are consistent with other studies showing that Cry2 is required for normal emotional behavior. Our findings confirm previous roles of Cry2 in behavior and extend them by showing that the effects on behavior may be mediated by changes in brain metabolism.
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http://dx.doi.org/10.1111/gbb.12708DOI Listing
April 2021

Association of neuroinflammation with episodic memory: a [C]PBR28 PET study in cognitively discordant twin pairs.

Brain Commun 2020 14;2(1):fcaa024. Epub 2020 Apr 14.

Turku PET Centre, University of Turku, Turku 20521, Finland.

Alzheimer's disease is associated with chronic response of innate immune system, referred as neuroinflammation. PET radioligands binding to the 18 kDa translocator protein are potential biomarkers of neuroinflammation. Translocator protein PET studies in mild cognitive impairment and Alzheimer's disease have indicated controversial results, possibly reflecting interindividual variation and heterogeneity of study populations. We controlled for genetic and environmental effects by studying twin pairs discordant for episodic memory performance. Episodic memory impairment is a well-known cognitive hallmark of early Alzheimer's disease process. Eleven same-sex twin pairs (four monozygotic pairs, six female pairs, age 72-77 years) underwent [C]-acetyl--(2-methoxybenzyl)-2-phenoxy-5-pyridinamine ([C]PBR28) PET imaging, structural magnetic resonance imaging and neuropsychological testing in 2014-17. Main PET outcome was the volume-weighted average standardized uptake value of cortical regions vulnerable to Alzheimer's disease pathology. Ten pairs were discordant for episodic memory performance. In the eight pairs with identical translocator protein genotype, twins with poorer episodic memory had ∼20% higher cortical [C]PBR28 binding compared with their better-performing co-twins (mean intra-pair difference 0.21 standardized uptake value, 95% confidence interval 0.05-0.37,  = 0.017). The result remained the same when including all discordant pairs and controlling for translocator protein genotype. Increased translocator protein PET signal suggests that increased microglial activation is associated with poorer episodic memory performance. Twins with worse episodic memory performance compared with their co-twins had on average 20% higher uptake of the neuroinflammatory marker translocator protein PET tracer [C]PBR28. The findings support a negative association between neuroinflammation and episodic memory and the use of translocator protein positron emission tomography as a useful indicator of Alzheimer's disease process.
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http://dx.doi.org/10.1093/braincomms/fcaa024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7425350PMC
April 2020

Radiosynthesis and preclinical evaluation of [Ga]Ga-NOTA-folate for PET imaging of folate receptor β-positive macrophages.

Sci Rep 2020 08 12;10(1):13593. Epub 2020 Aug 12.

Turku PET Centre, University of Turku, Kiinamyllynkatu 4-8, 20520, Turku, Finland.

Folate receptor β (FR-β), a marker expressed on macrophages, is a promising target for imaging of inflammation. Here, we report the radiosynthesis and preclinical evaluation of [Ga]Ga-NOTA-folate (Ga-FOL). After determining the affinity of Ga-FOL using cells expressing FR-β, we studied atherosclerotic mice with Ga-FOL and F-FDG PET/CT. In addition, we studied tracer distribution and co-localization with macrophages in aorta cryosections using autoradiography, histology, and immunostaining. The specificity of Ga-FOL was assessed in a blocking study with folate glucosamine. As a final step, human radiation doses were extrapolated from rat PET data. We were able to produce Ga-FOL with high radiochemical purity and moderate molar activity. Cell binding studies revealed that Ga-FOL had 5.1 nM affinity for FR-β. Myocardial uptake of Ga-FOL was 20-fold lower than that of F-FDG. Autoradiography and immunohistochemistry of the aorta revealed that Ga-FOL radioactivity co-localized with Mac-3-positive macrophage-rich atherosclerotic plaques. The plaque-to-healthy vessel wall ratio of Ga-FOL was significantly higher than that of F-FDG. Blocking studies verified that Ga-FOL was specific for FR. Based on estimations from rat data, the human effective dose was 0.0105 mSv/MBq. Together, these findings show that Ga-FOL represents a promising new FR-β-targeted tracer for imaging macrophage-associated inflammation.
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http://dx.doi.org/10.1038/s41598-020-70394-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7423886PMC
August 2020

Folate Receptor β-Targeted PET Imaging of Macrophages in Autoimmune Myocarditis.

J Nucl Med 2020 11 13;61(11):1643-1649. Epub 2020 Apr 13.

Turku PET Centre, University of Turku, Turku, Finland

Currently available imaging techniques have limited specificity for the detection of active myocardial inflammation. Aluminum F-labeled 1,4,7-triazacyclononane--triacetic acid conjugated folate (F-FOL) is a PET tracer targeting folate receptor β (FR-β), which is expressed on activated macrophages at sites of inflammation. We evaluated F-FOL PET for the detection of myocardial inflammation in rats with autoimmune myocarditis and studied the expression of FR-β in human cardiac sarcoidosis specimens. Myocarditis was induced by immunizing rats ( = 18) with porcine cardiac myosin in complete Freund adjuvant. Control rats ( = 6) were injected with Freund adjuvant alone. F-FOL was intravenously injected, followed by imaging with a small-animal PET/CT scanner and autoradiography. Contrast-enhanced high-resolution CT or F-FDG PET images were used for coregistration. Rat tissue sections and myocardial autopsy samples from 6 patients with cardiac sarcoidosis were studied for macrophages and FR-β. The myocardium of 10 of 18 immunized rats showed focal macrophage-rich inflammatory lesions, with FR-β expression occurring mainly in M1-polarized macrophages. PET images showed focal myocardial F-FOL uptake colocalizing with inflammatory lesions (SUV, 2.1 ± 1.1), whereas uptake in the remote myocardium of immunized rats and controls was low (SUV, 0.4 ± 0.2 and 0.4 ± 0.1, respectively; < 0.01). Ex vivo autoradiography of tissue sections confirmed uptake of F-FOL in myocardial inflammatory lesions. Uptake of F-FOL in inflamed myocardium was efficiently blocked by a nonlabeled FR-β ligand folate glucosamine in vivo. The myocardium of patients with cardiac sarcoidosis showed many FR-β-positive macrophages in inflammatory lesions. In a rat model of autoimmune myocarditis, F-FOL shows specific uptake in inflamed myocardium containing macrophages expressing FR-β, which were also present in human cardiac sarcoid lesions. Imaging of FR-β expression is a potential approach for the detection of active myocardial inflammation.
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http://dx.doi.org/10.2967/jnumed.119.241356DOI Listing
November 2020

Elevated serum chemokine CCL22 levels in first-episode psychosis: associations with symptoms, peripheral immune state and in vivo brain glial cell function.

Transl Psychiatry 2020 03 16;10(1):94. Epub 2020 Mar 16.

Finnish Institute for Health and Welfare, Mental Health Unit, Helsinki, Finland.

Several lines of research support immune system dysregulation in psychotic disorders. However, it remains unclear whether the immunological marker alterations are stable and how they associate with brain glial cell function. This longitudinal study aimed at investigating whether peripheral immune functions are altered in the early phases of psychotic disorders, whether the changes are associated with core symptoms, remission, brain glial cell function, and whether they persist in a one-year follow-up. Two independent cohorts comprising in total of 129 first-episode psychosis (FEP) patients and 130 controls were assessed at baseline and at the one-year follow-up. Serum cyto-/chemokines were measured using a 38-plex Luminex assay. The FEP patients showed a marked increase in chemokine CCL22 levels both at baseline (p < 0.0001; Cohen's d = 0.70) and at the 12-month follow-up (p = 0.0007) compared to controls. The group difference remained significant (p = 0.0019) after accounting for relevant covariates including BMI, smoking, and antipsychotic medication. Elevated serum CCL22 levels were significantly associated with hallucinations (ρ = 0.20) and disorganization (ρ = 0.23), and with worse verbal performance (ρ = -0.23). Brain glial cell activity was indexed with positron emission tomography and the translocator protein radiotracer [C]PBR28 in subgroups of 15 healthy controls and 14 FEP patients with serum CCL22/CCL17 measurements. The distribution volume (V) of [C]PBR28 was lower in patients compared to controls (p = 0.026; Cohen's d = 0.94) without regionally specific effects, and was inversely associated with serum CCL22 and CCL17 levels (p = 0.036). Our results do not support the over-active microglia hypothesis of psychosis, but indicate altered CCR4 immune signaling in early psychosis with behavioral correlates possibly mediated through cross-talk between chemokine networks and dysfunctional or a decreased number of glial cells.
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http://dx.doi.org/10.1038/s41398-020-0776-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7075957PMC
March 2020

[F]SPA-RQ/PET Study of NK1 receptors in the Whole Body of Guinea Pig and Rat.

Sci Rep 2019 12 31;9(1):20412. Epub 2019 Dec 31.

Turku PET Centre, University of Turku, Turku, Finland.

There is a substantial interest in the development of NK1 substance P antagonists as potential treatments for various neuropsychiatric and somatic disorders. The aim of this study was to determine whether [F]SPA-RQ can be utilized as a tool for studying the whole body distribution and function of NK1 receptors in preclinical settings. The compound was injected into guinea pigs with or without premedication with a NK1 receptor antagonist (NK1A-2). For comparison, we included two rats in the study, as the affinity of antagonists for NK1 receptors is known to vary between species. The whole body biodistribution of the tracer was determined at several time points. The tracer showed specific binding in organs compatible with the known location of NK1-receptors. Premedication with a NK1 antagonist led to an inhibited uptake of [F]SPA-RQ in several organs of guinea pigs, notably intestine, pancreas, urinary bladder, uterus, skin and lung. Specific binding was also seen in both cortex and striatum. In contrast, negligible specific binding was observed in the rat brain with [F]SPA-RQ, whereas the tracer uptake in peripheral tissues was similar to that seen in guinea pigs. We conclude that [F]SPA-RQ/PET is a useful tool to study the distribution and function of peripherally located NK1 receptors e.g. in different disease models.
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http://dx.doi.org/10.1038/s41598-019-56848-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6938475PMC
December 2019

Folate receptor-targeted positron emission tomography of experimental autoimmune encephalomyelitis in rats.

J Neuroinflammation 2019 Dec 3;16(1):252. Epub 2019 Dec 3.

Turku PET Centre, University of Turku, Turku, Finland.

Background: Folate receptor-β (FR-β) is a cell surface receptor that is significantly upregulated on activated macrophages during inflammation and provides a potential target for folate-based therapeutic and diagnostic agents. FR-β expression in central nervous system inflammation remains relatively unexplored. Therefore, we used focally induced acute and chronic phases of experimental autoimmune encephalomyelitis (EAE) to study patterns of FR-β expression and evaluated its potential as an in vivo imaging target.

Methods: Focal EAE was induced in rats using heat-killed Bacillus Calmette-Guérin followed by activation with complete Freund's adjuvant supplemented with Mycobacterium tuberculosis. The rats were assessed with magnetic resonance imaging and positron emission tomography/computed tomography (PET/CT) at acute (14 days) and chronic (90 days) phases of inflammation. The animals were finally sacrificed for ex vivo autoradiography of their brains. PET studies were performed using FR-β-targeting aluminum [F]fluoride-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid conjugated folate ([F]AlF-NOTA-folate, F-FOL) and 18 kDa translocator protein (TSPO)-targeting N-acetyl-N-(2-[C]methoxybenzyl)-2-phenoxy-5-pyridinamine (C-PBR28). Post-mortem immunohistochemistry was performed using anti-FR-β, anti-cluster of differentiation 68 (anti-CD68), anti-inducible nitric oxide synthase (anti-iNOS), and anti-mannose receptor C-type 1 (anti-MRC-1) antibodies. The specificity of F-FOL binding was verified using in vitro brain sections with folate glucosamine used as a blocking agent.

Results: Immunohistochemical evaluation of focal EAE lesions demonstrated anti-FR-β positive cells at the lesion border in both acute and chronic phases of inflammation. We found that anti-FR-β correlated with anti-CD68 and anti-MRC-1 immunohistochemistry; for MRC-1, the correlation was most prominent in the chronic phase of inflammation. Both F-FOL and C-PBR28 radiotracers bound to the EAE lesions. Autoradiography studies verified that this binding took place in areas of anti-FR-β positivity. A blocking assay using folate glucosamine further verified the tracer's specificity. In the chronic phase of EAE, the lesion-to-background ratio of F-FOL was significantly higher than that of C-PBR28 (P = 0.016).

Conclusion: Our EAE results imply that FR-β may be a useful target for in vivo imaging of multiple sclerosis-related immunopathology. FR-β-targeted PET imaging with F-FOL may facilitate the monitoring of lesion development and complement the information obtained from TSPO imaging by bringing more specificity to the PET imaging armamentarium for neuroinflammation.
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http://dx.doi.org/10.1186/s12974-019-1612-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6892159PMC
December 2019

Fibroblast Growth Factor 21 Drives Dynamics of Local and Systemic Stress Responses in Mitochondrial Myopathy with mtDNA Deletions.

Cell Metab 2019 12 12;30(6):1040-1054.e7. Epub 2019 Sep 12.

Stem Cells and Metabolism Research Program, Faculty of Medicine, University of Helsinki, 00290 Helsinki, Finland; Department of Neurosciences, Helsinki University Central Hospital, 00290 Helsinki, Finland; Neuroscience Center, University of Helsinki, 00290 Helsinki, Finland. Electronic address:

Mitochondrial dysfunction elicits stress responses that safeguard cellular homeostasis against metabolic insults. Mitochondrial integrated stress response (ISR) is a major response to mitochondrial (mt)DNA expression stress (mtDNA maintenance, translation defects), but the knowledge of dynamics or interdependence of components is lacking. We report that in mitochondrial myopathy, ISR progresses in temporal stages and development from early to chronic and is regulated by autocrine and endocrine effects of FGF21, a metabolic hormone with pleiotropic effects. Initial disease signs induce transcriptional ISR (ATF5, mitochondrial one-carbon cycle, FGF21, and GDF15). The local progression to 2 metabolic ISR stage (ATF3, ATF4, glucose uptake, serine biosynthesis, and transsulfuration) is FGF21 dependent. Mitochondrial unfolded protein response marks the 3 ISR stage of failing tissue. Systemically, FGF21 drives weight loss and glucose preference, and modifies metabolism and respiratory chain deficiency in a specific hippocampal brain region. Our evidence indicates that FGF21 is a local and systemic messenger of mtDNA stress in mice and humans with mitochondrial disease.
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http://dx.doi.org/10.1016/j.cmet.2019.08.019DOI Listing
December 2019

Effects of age, BMI and sex on the glial cell marker TSPO - a multicentre [C]PBR28 HRRT PET study.

Eur J Nucl Med Mol Imaging 2019 Oct 30;46(11):2329-2338. Epub 2019 Jul 30.

Centre for Psychiatry Research, Department of Clinical Neuroscience, Karolinska Institutet and Stockholm County, Stockholm, Sweden.

Purpose: The purpose of this study was to investigate the effects of ageing, sex and body mass index (BMI) on translocator protein (TSPO) availability in healthy subjects using positron emission tomography (PET) and the radioligand [C]PBR28.

Methods: [C]PBR28 data from 140 healthy volunteers (72 males and 68 females; N = 78 with HAB and N = 62 MAB genotype; age range 19-80 years; BMI range 17.6-36.9) were acquired with High Resolution Research Tomograph at three centres: Karolinska Institutet (N = 53), Turku PET centre (N = 62) and Yale University PET Center (N = 25). The total volume of distribution (V) was estimated in global grey matter, frontal, temporal, occipital and parietal cortices, hippocampus and thalamus using multilinear analysis 1. The effects of age, BMI and sex on TSPO availability were investigated using linear mixed effects model, with TSPO genotype and PET centre specified as random intercepts.

Results: There were significant positive correlations between age and V in the frontal and temporal cortex. BMI showed a significant negative correlation with V in all regions. Additionally, significant differences between males and females were observed in all regions, with females showing higher V. A subgroup analysis revealed a positive correlation between V and age in all regions in male subjects, whereas age showed no effect on TSPO levels in female subjects.

Conclusion: These findings provide evidence that individual biological properties may contribute significantly to the high variation shown in TSPO binding estimates, and suggest that age, BMI and sex can be confounding factors in clinical studies.
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http://dx.doi.org/10.1007/s00259-019-04403-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6717599PMC
October 2019

Aluminum fluoride-18 labeled folate enables in vivo detection of atherosclerotic plaque inflammation by positron emission tomography.

Sci Rep 2018 06 26;8(1):9720. Epub 2018 Jun 26.

Turku PET Centre, University of Turku, Turku, Finland.

Inflammation plays an important role in the development of atherosclerosis and its complications. Because the folate receptor β (FR-β) is selectively expressed on macrophages, an FR targeted imaging agent could be useful for assessment of atherosclerotic inflammation. We investigated aluminum fluoride-18-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid conjugated folate (F-FOL) for the detection of atherosclerotic plaque inflammation. We studied atherosclerotic plaques in mice, rabbits, and human tissue samples using F-FOL positron emission tomography/computed tomography (PET/CT). Compound 2-deoxy-2-[F]fluoro-D-glucose (F-FDG) was used as a comparison. Firstly, we found that the in vitro binding of F-FOL co-localized with FR-β-positive macrophages in carotid endarterectomy samples from patients with recent ischemic symptoms. We then demonstrated specific accumulation of intravenously administered F-FOL in atherosclerotic plaques in mice and rabbits using PET/CT. We noticed that the F-FOL uptake correlated with the density of macrophages in plaques and provided a target-to-background ratio as high as F-FDG, but with considerably lower myocardial uptake. Thus, F-FOL PET/CT targeting of FR-β-positive macrophages presents a promising new tool for the in vivo imaging of atherosclerotic inflammation.
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http://dx.doi.org/10.1038/s41598-018-27618-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6018703PMC
June 2018

Vascular adhesion protein-1 is actively involved in the development of inflammatory lesions in rat models of multiple sclerosis.

J Neuroinflammation 2018 May 1;15(1):128. Epub 2018 May 1.

Turku PET Centre, University of Turku, Kiinamyllynkatu 4-8, FI-20520, Turku, Finland.

Background: Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible endothelial cell molecule and primary amine oxidase that mediates leukocyte entry to sites of inflammation. However, there is limited knowledge of the inflammation-related expression of VAP-1 in the central nervous system (CNS). Therefore, we investigated the expression of VAP-1 within the CNS vasculature in two focal rat models of experimental autoimmune encephalomyelitis (EAE) mimicking multiple sclerosis (MS).

Methods: EAE was induced either with Bacillus Calmette-Guérin, resulting in a delayed-type hypersensitivity-like pathogenesis (fDTH-EAE), or with myelin oligodendrocyte glycoprotein (fMOG-EAE). A subgroup of fMOG-EAE rats were treated daily with a selective VAP-1 inhibitor (LJP1586; 5 mg/kg). On 3 and 14 days after lesion activation, rat brains were assessed using magnetic resonance imaging (MRI), and ex vivo autoradiography was conducted to evaluate the binding of Gallium-68-labelled VAP-1 ligand. Histology and immunohistochemistry (OX-42, VAP-1, intercellular adhesion protein-1 [ICAM-1], P-selectin) supported the ex vivo autoradiography.

Results: EAE lesions showed MRI-detectable signal changes and binding of the VAP-1-targeting radiotracer in both rat models. Some of the VAP-1 positive vessels showed morphological features typical for high endothelial-like venules at sites of inflammation. Inhibition of VAP-1 activity with small molecule inhibitor, LJP1586, decreased lymphocyte density in the acute inflammatory phase of fMOG-EAE lesions (day 3, P = 0.026 vs. untreated), but not in the remission phase (day 14, P = 0.70 vs. untreated), and had no effect on the amount of OX-42-positive cells in either phase. LJP1586 treatment reduced VAP-1 and ICAM-1 expression in the acute inflammatory phase, whereas P-selectin remained not detectable at all studied stages of the disease.

Conclusions: Our results revealed that VAP-1 is expressed and functionally active in vasculature within the induced focal EAE lesions during the acute phase of inflammation and remains expressed after the acute inflammation has subsided. The study indicates that VAP-1 is actively involved in the development of inflammatory CNS lesions. During this process, the endothelial cell lesion-related vasculature seem to undergo a structural transformation from regular flat-walled endothelium to HEV-like endothelium.
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http://dx.doi.org/10.1186/s12974-018-1152-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5930736PMC
May 2018

F-labeled norepinephrine transporter tracer [F]NS12137: radiosynthesis and preclinical evaluation.

Nucl Med Biol 2018 Jan 24;56:39-46. Epub 2017 Oct 24.

Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Turku, Finland; Department of Chemistry, University of Turku, Turku, Finland; Accelerator Laboratory, Åbo Akademi University, Turku, Finland.

Introduction: Several psychiatric and neurodegenerative diseases are associated with malfunction of brain norepinephrine transporter (NET). However, current clinical evaluations of NET function are limited by the lack of sufficiently sensitive methods of detection. To this end, we have synthesized exo-3-[(6-[F]fluoro-2-pyridyl)oxy]-8-azabicyclo[3.2.1]-octane ([F]NS12137) as a radiotracer for positron emission tomography (PET) and have demonstrated that it is highly specific for in vivo detection of NET-rich regions of rat brain tissue.

Methods: We applied two methods of electrophilic, aromatic radiofluorination of the precursor molecule, exo-3-[(6-trimethylstannyl-2-pyridyl)oxy]-8-azabicyclo-[3.2.1]octane-8-carboxylate: (1) direct labeling with [F]F, and (2) labeling with [F]Selectfluor, a derivative of [F]F, using post-target produced [F]F. The time-dependent distribution of [F]NS12137 in brain tissue of healthy, adult Sprague-Dawley rats was determined by ex vivo autoradiography. The specificity of [F]NS12137 binding was demonstrated on the basis of competitive binding by nisoxetine, a known NET antagonist of high specificity.

Results: [F]NS12137 was successfully synthesized with radiochemical yields of 3.9% ± 0.3% when labeled with [F]F and 10.2% ± 2.7% when labeled with [F]Selectfluor. The molar activity of radiotracer was 8.8 ± 0.7 GBq/μmol with [F]F labeling and 6.9 ± 0.4 GBq/μmol with [F]Selectfluor labeling at the end of synthesis of [F]NS12137. Uptake of [F]NS12137 in NET-rich areas in rat brain was demonstrated with the locus coeruleus (LCoe) having the highest regional uptake. Prior treatment of rats with nisoxetine showed no detectable [F]NS12137 in the LCoe. Analyses of whole brain samples for radiometabolites showed only the parent compound [F]NS12137. Uptake of F-radioactivity in bone increased with time.

Conclusions: The two electrophilic F-labeling methods proved to be suitable for synthesis of [F]NS12137 with the [F]Selectfluor method providing an approximate three-fold higher yield than the [F]F method. As an electrostatically neutral radiotracer [F]NS12137 crosses the blood-brain barrier and enabled specific labeling of NET-rich regions of rat brain tissue with the highest concentration in the LCoe.
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http://dx.doi.org/10.1016/j.nucmedbio.2017.10.005DOI Listing
January 2018

Somatostatin receptor expression in lymphomas: a source of false diagnosis of neuroendocrine tumor at Ga-DOTANOC PET/CT imaging.

Acta Oncol 2018 Feb 7;57(2):283-289. Epub 2017 Jul 7.

b Turku PET Centre, Turku University Hospital, University of Turku , Turku , Finland.

Background: Ga-DOTANOC PET/CT is routinely used to image neuroendocrine tumors (NETs). A case of lymphoma initially thought to be NET based on a positive Ga-DOTANOC PET/CT was recently seen at our institution. This prompted us to determine prospectively somatostatin receptor (SSTR) status in patients with lymphoma by immunohistochemical analysis of SSTR subtypes 2, 3 and 5 (SSTR) and Ga-DOTANOC PET/CT imaging.

Material And Methods: Twenty-one patients with newly diagnosed lymphoma were referred to Ga-DOTANOC and FDG PET/CT prior to any treatment. Tracer uptake was evaluated visually by two nuclear medicine specialists. Maximum standardized uptake values (SUVmax) were determined from 14 nodal and two extranodal regions with highest uptake in each patient. Lesions were then graded with Deauville score (1-5) on FDG PET/CT and modified Krenning score (0-4) on Ga-DOTANOC PET/CT, respectively. SSTR status was analyzed from routine biopsies of lymphomatous tissue and matched to corresponding PET/CT findings.

Results: About 20/21 patients had FDG-positive lymphoma (Deauville score ≥3). Uptake of Ga-DOTANOC was regarded as positive if Krenning score was ≥2 and resulted in 13/21 (62%) patients having Ga-DOTANOC-positive lymphomas. The highest uptake of Ga-DOTANOC was seen in Hodgkin's lymphoma of nodular sclerosis subtype and in diffuse large B-cell lymphoma (SUVmax median 9.8 and 9.7, respectively). Both cases showed strong SSTR immunopositivity in tumor cells. Some patients had SSTR immunopositivity predominantly in endothelial and dendritic cells and follicular centers of lymph nodes contributing to a positive PET/CT with probably low tumor-specific uptake. SSTR and SSTR were negative in most lymphoma subtypes.

Conclusions: According to this pilot study, Ga-DOTANOC PET/CT is positive in some lymphoma subtypes which express SSTRs. These tumors present a potential risk of being misinterpreted as NETs if a representative tumor sample is not available. Lymphomas with high expression of SSTRs may be amenable to treatments targeting these receptors.
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http://dx.doi.org/10.1080/0284186X.2017.1342864DOI Listing
February 2018

Ex Vivo Tracing of NMDA and GABA-A Receptors in Rat Brain After Traumatic Brain Injury Using 18F-GE-179 and 18F-GE-194 Autoradiography.

J Nucl Med 2016 09 19;57(9):1442-7. Epub 2016 May 19.

PET Preclinical Laboratory, Turku PET Centre, University of Turku, Turku, Finland Medicity Research Laboratory, University of Turku, Turku, Finland

Unlabelled: In vivo imaging of N-methyl-d-aspartate (NMDA) glutamate receptor and γ-aminobutyric acid (GABA)-A receptor during progression of brain pathology is challenging because of the lack of imaging tracers with high affinity and specificity.

Methods: We monitored changes in NMDA receptor and GABA-A receptor in a clinically relevant model of traumatic brain injury (TBI) induced by lateral fluid percussion in adult rats, using 2 new ligands for PET: (18)F-GE-179 for the open/active state of the NMDA receptor ion channel and (18)F-GE-194 for GABA-A receptor. Ex vivo brain autoradiography of radioligands was performed at subacute (5-6 d) and chronic (40-42 d) time points after TBI.

Results: At 5-6 d after TBI, (18)F-GE-179 binding was higher in the cortical lesion area, in the lesion core, and in the hippocampus than in the corresponding contralateral regions; this increase was probably related to increased permeability of the blood-brain barrier. At 40-42 d after TBI, (18)F-GE-179 binding was significantly higher in the medial cortex, in the corpus callosum, and in the thalamus than in the corresponding contralateral regions. Five to 6 days after TBI, (18)F-GE-194 binding was significantly higher in the lesion core and significantly lower in the ipsilateral thalamus. By 40-42 d after TBI, the reduction in (18)F-GE-194 binding extended to the cortical lesion, including the perilesional cortex around the lesion core. The reduction in thalamic binding was more extensive at 40-42 d than at 5-6 d after TBI, suggesting a progressive decrease in thalamic GABA-A receptor density. Immunohistochemistry against GABA-A α1 subunit revealed a similar decrease to (18)F-GE-194 binding, particularly during the chronic phase.

Conclusion: Our data support the validity of novel (18)F-GE-179 and (18)F-GE-194 radioligands for the detection of changes in active NMDA receptor and GABA-A receptor in the injured brain. These tools are useful for follow-up evaluation of secondary postinjury pathologies.
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http://dx.doi.org/10.2967/jnumed.115.167403DOI Listing
September 2016

Mitochondrial DNA Replication Defects Disturb Cellular dNTP Pools and Remodel One-Carbon Metabolism.

Cell Metab 2016 Apr 25;23(4):635-48. Epub 2016 Feb 25.

Research Programs Unit, Molecular Neurology, University of Helsinki, 00290 Helsinki, Finland; Department of Neurology, University of Helsinki, Helsinki University Hospital, 00290 Helsinki, Finland; Neuroscience Center, University of Helsinki, 00790 Helsinki, Finland. Electronic address:

Mitochondrial dysfunction affects cellular energy metabolism, but less is known about the consequences for cytoplasmic biosynthetic reactions. We report that mtDNA replication disorders caused by TWINKLE mutations-mitochondrial myopathy (MM) and infantile onset spinocerebellar ataxia (IOSCA)-remodel cellular dNTP pools in mice. MM muscle shows tissue-specific induction of the mitochondrial folate cycle, purine metabolism, and imbalanced and increased dNTP pools, consistent with progressive mtDNA mutagenesis. IOSCA-TWINKLE is predicted to hydrolyze dNTPs, consistent with low dNTP pools and mtDNA depletion in the disease. MM muscle also modifies the cytoplasmic one-carbon cycle, transsulfuration, and methylation, as well as increases glucose uptake and its utilization for de novo serine and glutathione biosynthesis. Our evidence indicates that the mitochondrial replication machinery communicates with cytoplasmic dNTP pools and that upregulation of glutathione synthesis through glucose-driven de novo serine biosynthesis contributes to the metabolic stress response. These results are important for disorders with primary or secondary mtDNA instability and offer targets for metabolic therapy.
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http://dx.doi.org/10.1016/j.cmet.2016.01.019DOI Listing
April 2016

Detecting a dexmedetomidine-evoked reduction of noradrenaline release in the human brain with the alpha2C-adrenoceptor PET ligand [11C]ORM-13070.

Synapse 2016 Feb 26;70(2):57-65. Epub 2015 Nov 26.

Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.

PET imaging can for some neurotransmitters be used to measure synaptic neurotransmitter concentrations. The objective of this study was to test whether the receptor binding of the α2C -AR antagonist PET tracer [(11)C]ORM-13070 would increase in response to reductions in synaptic noradrenaline, evoked by dexmedetomidine as a sympatholytic drug challenge. Six subjects underwent a control PET scan and two dexmedetomidine PET scans. Dexmedetomidine was infused with target plasma concentrations of 0.6 and 0.2 ng/ml. Tracer binding was measured by voxel-based analysis of bound per free (B/F) images. ROI-based analysis was performed in the dorsal striatum and in the thalamus. Vital signs and drug concentrations in plasma were measured and the sedative effect was estimated with the visual analog scale. In the voxel-based analysis, dexmedetomidine administration was associated with a tendency to increased B/F tracer in the right thalamus (mean, +17%, P = 0.14, and +19%, P = 0.05, with the low and high dose, respectively). Tracer binding in the dorsal striatum was unaffected by dexmedetomidine. A cluster with significantly increased B/F tracer (+42%, P = 0.01) was seen in the right superior temporal gyrus with low-dose dexmedetomidine, but not after the high dose. Brain uptake of [(11)C]ORM-13070 has previously been shown to be reduced in conditions of increased synaptic noradrenaline concentrations. In this study, tracer binding in the thalamus tended to increase in accordance with reduced activity of noradrenergic projections from the locus coeruleus, but statistical significance was not reached.
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http://dx.doi.org/10.1002/syn.21872DOI Listing
February 2016

In vivo PET imaging demonstrates diminished microglial activation after fingolimod treatment in an animal model of multiple sclerosis.

J Nucl Med 2015 Feb 8;56(2):305-10. Epub 2015 Jan 8.

Clinical Neurology, Turku PET Centre, University of Turku, Turku, Finland.

Unlabelled: There is a great need for the monitoring of microglial activation surrounding multiple sclerosis lesions because the activation of microglia is thought to drive widespread neuronal damage. Recently, second-generation PET radioligands that can reveal the extent of microglial activation by quantifying the increased expression of the 18-kDa translocator protein have been developed. Here, we investigate whether PET imaging can be used to demonstrate the reduction in microglial activation surrounding a chronic focal multiple sclerosis (MS)-like lesion after treatment with fingolimod, an established MS therapy.

Methods: Chronic focal experimental autoimmune encephalitis (EAE)-like lesions were induced in Lewis rats (n = 24) via stereotactic intrastriatal injection of heat-killed bacillus Calmette-Guérin (BCG) and subsequent activation using an intradermal injection of BCG in complete Freund adjuvant. This process resulted in a delayed-type hypersensitivity (DTH)-like EAE lesion. The extent of neuroinflammation surrounding the lesion was measured using (18)F-GE180 as a PET radioligand. The imaging was performed before and after treatment with fingolimod (0.3 mg/kg/d by mouth, 28 d) or vehicle as a control. In addition to imaging, autoradiography and immunohistochemistry experiments were performed to verify the in vivo results.

Results: The chronic DTH EAE lesion led to increased ligand binding in the ipsilateral, compared with contralateral, hemisphere when PET imaging was performed with the translocator protein-binding radioligand (18)F-GE180. Treatment with fingolimod led to a highly significant reduction in the binding potential, which could be demonstrated using both in vivo and ex vivo imaging (fingolimod vs. vehicle treatment, P < 0.0001). The area of increased (18)F-GE180 signal mapped closely to the area of activated microglial cells detected by immunohistochemistry.

Conclusion: PET imaging, unlike MR imaging, can be used to visualize the microglial activation surrounding a chronic DTH EAE lesion. Importantly, the treatment effect of fingolimod can be monitored in vivo by measuring the degree of microglial activation surrounding the chronic DTH EAE lesion. This work gives promise for the introduction of new outcome measures applicable in treatment studies of progressive MS.
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http://dx.doi.org/10.2967/jnumed.114.149955DOI Listing
February 2015

Amphetamine decreases α2C-adrenoceptor binding of [11C]ORM-13070: a PET study in the primate brain.

Int J Neuropsychopharmacol 2014 Dec 13;18(3). Epub 2014 Dec 13.

Karolinska Institutet, Department of Clinical Neuroscience, Center for Psychiatric Research, Stockholm, Sweden (Drs Finnema, Stepanov, Nakao, Varnäs, Varrone, Farde, and Halldin); Pfizer, Neuroscience Research Unit, Cambridge, MA (Drs Hughes, Babalola, and Grimwood); University of Turku, Turku PET Centre, Turku, Finland (Drs Haaparanta-Solin, Arponen, Marjamäki, and Solin); University of Turku, Department of Pharmacology, Drug Development and Therapeutics, and Turku University Hospital, Unit of Clinical Pharmacology, Turku, Finland (Drs Pohjanoksa, Vuorilehto, and Scheinin); Orion Corporation, Orion Pharma, Research and Development, Turku, Finland (Dr Sallinen); AstraZeneca, Translational Science Center at Karolinska Institutet, Stockholm, Sweden (Dr Farde).

Background: The neurotransmitter norepinephrine has been implicated in psychiatric and neurodegenerative disorders. Examination of synaptic norepinephrine concentrations in the living brain may be possible with positron emission tomography (PET), but has been hampered by the lack of suitable radioligands.

Methods: We explored the use of the novel α2C-adrenoceptor antagonist PET tracer [(11)C]ORM-13070 for measurement of amphetamine-induced changes in synaptic norepinephrine. The effect of amphetamine on [(11)C]ORM-13070 binding was evaluated ex vivo in rat brain sections and in vivo with PET imaging in monkeys.

Results: Microdialysis experiments confirmed amphetamine-induced elevations in rat striatal norepinephrine and dopamine concentrations. Regional [(11)C]ORM-13070 receptor binding was high in the striatum and low in the cerebellum. After injection of [(11)C]ORM-13070 in rats, mean striatal specific binding ratios, determined using cerebellum as a reference region, were 1.4±0.3 after vehicle pretreatment and 1.2±0.2 after amphetamine administration (0.3mg/kg, subcutaneous). Injection of [(11)C]ORM-13070 in non-human primates resulted in mean striatal binding potential (BP ND) estimates of 0.65±0.12 at baseline. Intravenous administration of amphetamine (0.5 and 1.0mg/kg, i.v.) reduced BP ND values by 31-50%. Amphetamine (0.3mg/kg, subcutaneous) increased extracellular norepinephrine (by 400%) and dopamine (by 270%) in rat striata.

Conclusions: Together, these results indicate that [(11)C]ORM-13070 may be a useful tool for evaluation of synaptic norepinephrine concentrations in vivo. Future studies are required to further understand a potential contribution of dopamine to the amphetamine-induced effect.
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http://dx.doi.org/10.1093/ijnp/pyu081DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4360244PMC
December 2014

A PET Tracer for Brain α2C Adrenoceptors, (11)C-ORM-13070: Radiosynthesis and Preclinical Evaluation in Rats and Knockout Mice.

J Nucl Med 2014 Jul 5;55(7):1171-7. Epub 2014 May 5.

Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Turku, Finland Accelerator Laboratory, Åbo Akademi University, Turku, Finland

Unlabelled: We report the development of a PET tracer for α2C adrenoceptor imaging and its preliminary preclinical evaluation. α2C adrenoceptors in the human brain may be involved in various neuropsychiatric disorders, such as depression, schizophrenia, and neurodegenerative diseases. PET tracers are needed for imaging of this receptor system in vivo.

Methods: High-specific-activity (11)C-ORM-13070 (1-[(S)-1-(2,3-dihydrobenzo[1,4]dioxin-2-yl)methyl]-4-(3-(11)C-methoxymethylpyridin-2-yl)-piperazine) was synthesized by (11)C-methylation of O-desmethyl-ORM-13070 with (11)C-methyl triflate, which was prepared from cyclotron-produced (11)C-methane via (11)C-methyl iodide. Rats and mice were investigated in vivo with PET and ex vivo with autoradiography. The specificity of (11)C-ORM-13070 binding to α2 adrenoceptors was demonstrated in rats pretreated with atipamezole, an α2 adrenoceptor antagonist. The α2C adrenoceptor selectivity of the tracer was determined by comparing tracer binding in wild-type and α2A- and α2AC adrenoceptor knockout (KO) mice. (11)C-ORM-13070 and its radioactive metabolites in rat plasma and brain tissue were analyzed with radio-high-performance liquid chromatography and mass spectroscopy. Human radiation dose estimates were extrapolated from rat biodistribution data.

Results: The radiochemical yield, calculated from initial cyclotron-produced (11)C-methane, was 9.6% ± 2.7% (decay-corrected to end of bombardment). The specific activity of the product was 640 ± 390 GBq/μmol (decay-corrected to end of synthesis). The radiochemical purity exceeded 99% in all syntheses. The highest levels of tracer binding were observed in the striatum and olfactory tubercle of rats and control and α2A KO mice-that is, in the brain regions known to contain the highest densities of α2C adrenoceptors. In rats pretreated with atipamezole and in α2AC KO mice, (11)C tracer binding in the striatum and olfactory tubercle was low, similar to that of the frontal cortex and thalamus, regions with low densities of α2C adrenoceptors. Two radioactive metabolites were found in rat plasma, but only one of them was found in the brain; their identity was not revealed. The estimated effective radiation dose was comparable with the average exposure level in PET studies with (11)C tracers.

Conclusion: An efficient method for the radiosynthesis of (11)C-ORM-13070 was developed. (11)C-ORM-13070 emerged as a potential novel radiotracer for in vivo imaging of brain α2C adrenoceptors.
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http://dx.doi.org/10.2967/jnumed.113.135574DOI Listing
July 2014

Detection of microglial activation in an acute model of neuroinflammation using PET and radiotracers 11C-(R)-PK11195 and 18F-GE-180.

J Nucl Med 2014 Mar 10;55(3):466-72. Epub 2014 Feb 10.

Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Turku, Finland.

Unlabelled: It remains unclear how different translocator protein (TSPO) ligands reflect the spatial extent of astrocyte or microglial activation in various neuroinflammatory conditions. Here, we use a reproducible lipopolysaccharide (LPS)-induced model of acute central nervous system inflammation to compare the binding performance of a new TSPO ligand (18)F-GE-180 with (11)C-(R)-PK11195. Using immunohistochemistry, we also explore the ability of the TSPO ligands to detect activated microglial cells and astrocytes.

Methods: Lewis rats (n = 30) were microinjected with LPS (1 or 10 μg) or saline (1 μL) into the left striatum. The animals were imaged in vivo at 16 h after the injection using PET radiotracers (18)F-GE-180 or (11)C-(R)-PK11195 (n = 3 in each group) and were killed afterward for autoradiography of the brain. Immunohistochemical assessment of OX-42 and glial fibrillary acidic protein (GFAP) was performed to identify activated microglial cells and reactive astrocytes.

Results: In vivo PET imaging revealed an increase in the ipsilateral TSPO binding, compared with binding in the contralateral hemisphere, after the microinjection of 10 μg of LPS. No increase was observed with vehicle. By autoradiography, the TSPO radiotracer binding potential in the injected hemisphere was increased after striatal injection of 1 or 10 μg of LPS. However, the significant increase was observed only when using (18)F-GE-180. The area of CD11b-expressing microglial cells extended beyond that of enhanced GFAP staining and mapped more closely to the extent of (18)F-GE-180 binding than to (11)C-(R)-PK11195 binding. The signal from either PET ligand was significantly increased in regions of increased GFAP immunoreactivity and OX-42 colocalization, meaning that the presence of both activated microglia and astrocytes in a given area leads to increased binding of the TSPO radiotracers.

Conclusion: (18)F-GE-180 is able to reveal sites of activated microglia in both gray and white matter. However, the signal is increased by the presence of activated astrocytes. Therefore, (18)F-GE-180 is a promising new fluorinated longer-half-life tracer that reveals the presence of activated microglia in a manner that is superior to (11)C-(R)-PK11195 due to the higher binding potential observed for this ligand.
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http://dx.doi.org/10.2967/jnumed.113.125625DOI Listing
March 2014

[18F]CFT synthesis and binding to monoamine transporters in rats.

EJNMMI Res 2012 Jan 25;2(1). Epub 2012 Jan 25.

Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Porthaninkatu 3, Turku, 20500, Finland.

Background: We present the electrophilic synthesis of [18F]2β-carbomethoxy-3β-(4-fluoro)tropane [[18F]CFT] and the pharmacological specificity and selectivity of [18F]CFT for monoamine transporters in the brain and peripheral organs of rats. The human radiation dose is extrapolated from the animal data.

Methods: [18F]CFT was synthesized by electrophilic fluorination of a stannylated precursor by using post-target-produced [18F]F2 as a fluorinating agent. The ex vivo 18F-activity biodistribution of [18F]CFT in the brain of rats was studied by autoradiography. The binding of [18F]CFT to the monoamine transporters was studied using in vivo blocking experiments with dopamine transporter [DAT], norepinephrine transporter [NET], or serotonin transporter [SERT] inhibitors. In vivo animal positron emission tomography was used as a comparative method to determine tracer kinetics. Human radiation dose was assessed using OLINDA software.

Results: The radiochemical yield of [18F]CFT from the initial [18F]F-, decay corrected to the end of bombardment, was 3.2 ± 1.0%. The specific activity [SA] was 14.5 ± 3.4 GBq/μmol, decay corrected to the end of synthesis. Radiochemical purity exceeded 99%. DAT-specific binding was found in the striatum, locus coeruleus, and pancreas. NET-specific binding was found in the locus coeruleus. SERT-specific binding was not found in any of the studied organs. Effective dose equivalent [EDE] estimated for the standard human model was 12.8 μSv/MBq. Effective dose [ED] was 9.17 μSv/MBq.

Conclusions: Post-target-produced high-SA [18F]F2 was used to incorporate18F directly into the phenyl ring of [18F]CFT. The final product had high radiochemical and chemical purities and a high SA for DAT and NET studies in vivo. In periphery, [18F]CFT showed a specific uptake in the pancreas. EDE and ED corresponded well with other18F-radioligands.
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http://dx.doi.org/10.1186/2191-219X-2-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3299608PMC
January 2012

Novel electrophilic synthesis of 6-[¹⁸F]fluorodopamine and comprehensive biological evaluation.

Eur J Nucl Med Mol Imaging 2012 May 10;39(5):800-10. Epub 2012 Jan 10.

Turku PET Centre, University of Turku, Radiopharmaceutical Chemistry Laboratory, Kiinamyllynkatu 4-8, 20520, Turku, Finland.

Purpose: 6-[(18)F]Fluorodopamine (4-(2-aminoethyl)-5-[(18)F]fluorobenzene-1,2-diol, 6-[(18)F]FDA) is a tracer for imaging sympathetically innervated tissues. Previous electrophilic labelling methods produced 6-[(18)F]FDA with low specific radioactivity (SA) which has limited its wider use. Our aim was to employ electrophilic labelling and increase the SA to around 15 GBq/μmol. We also sought to determine an extensive biodistribution pattern for 6-[(18)F]FDA in rats in order to thoroughly identify tissues with dense sympathetic innervation that were specifically labelled with 6-[(18)F]FDA. In addition, to investigate the safety profile of 6-[(18)F]FDA in larger animals, we performed in vivo studies in pigs.

Methods: 6-[(18)F]FDA was synthesised using high SA electrophilic [(18)F]F(2) as the labelling reagent. Biodistribution and metabolism of 6-[(18)F]FDA was determined ex vivo in rats, and in vivo studies were done in pigs.

Results: 6-[(18)F]FDA was synthesised with 2.6 ± 1.1% radiochemical yield. The total amount of purified 6-[(18)F]FDA was 663 ± 291 MBq at the end of synthesis (EOS). SA, decay corrected to EOS, was 13.2 ± 2.7 GBq/μmol. Radiochemical purity exceeded 99.0%. Specific uptake of 6-[(18)F]FDA was demonstrated in heart, lung, pancreas, adrenal gland, lower large intestine (LLI), eye, thyroid gland, spleen and stomach tissue. 6-[(18)F]FDA in rat plasma declined rapidly, with a half-life of 2 min, indicating fast metabolism. In vivo PET studies in pigs confirmed the tracer could be used safely without pharmacological effects.

Conclusion: 6-[(18)F]FDA was synthesised with good radiopharmaceutical quality and yields high enough for several human PET studies. The SA of 6-[(18)F]FDA was improved by 50- to 500-fold compared to previous electrophilic methods. Uptake of 6-[(18)F]FDA was specific in various peripheral organs, indicating that 6-[(18)F]FDA PET can be used to investigate sympathoneural functions beyond cardiac studies when higher specific uptake is achieved.
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http://dx.doi.org/10.1007/s00259-011-2032-5DOI Listing
May 2012

Fast growth associated with aberrant vasculature and hypoxia in fibroblast growth factor 8b (FGF8b) over-expressing PC-3 prostate tumour xenografts.

BMC Cancer 2010 Oct 30;10:596. Epub 2010 Oct 30.

Institute of Biomedicine, Department of Cell Biology and Anatomy, University of Turku, Turku, Finland.

Background: Prostate tumours are commonly poorly oxygenated which is associated with tumour progression and development of resistance to chemotherapeutic drugs and radiotherapy. Fibroblast growth factor 8b (FGF8b) is a mitogenic and angiogenic factor, which is expressed at an increased level in human prostate tumours and is associated with a poor prognosis. We studied the effect of FGF8b on tumour oxygenation and growth parameters in xenografts in comparison with vascular endothelial growth factor (VEGF)-expressing xenografts, representing another fast growing and angiogenic tumour model.

Methods: Subcutaneous tumours of PC-3 cells transfected with FGF8b, VEGF or empty (mock) vectors were produced and studied for vascularity, cell proliferation, glucose metabolism and oxygenation. Tumours were evaluated by immunohistochemistry (IHC), flow cytometry, use of radiolabelled markers of energy metabolism ([18F]FDG) and hypoxia ([18F]EF5), and intratumoral polarographic measurements of pO2.

Results: Both FGF8b and VEGF tumours grew rapidly in nude mice and showed highly vascularised morphology. Perfusion studies, pO2 measurements, [18F]EF5 and [18F]FDG uptake as well as IHC staining for glucose transport protein (GLUT1) and hypoxia inducible factor (HIF) 1 showed that VEGF xenografts were well-perfused and oxygenised, as expected, whereas FGF8b tumours were as hypoxic as mock tumours. These results suggest that FGF8b-induced tumour capillaries are defective. Nevertheless, the growth rate of hypoxic FGF8b tumours was highly increased, as that of well-oxygenised VEGF tumours, when compared with hypoxic mock tumour controls.

Conclusion: FGF8b is able to induce fast growth in strongly hypoxic tumour microenvironment whereas VEGF-stimulated growth advantage is associated with improved perfusion and oxygenation of prostate tumour xenografts.
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http://dx.doi.org/10.1186/1471-2407-10-596DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2984431PMC
October 2010

Uptake of 11C-choline in mouse atherosclerotic plaques.

J Nucl Med 2010 May 15;51(5):798-802. Epub 2010 Apr 15.

Turku PET Centre, University of Turku, Turku, Finland.

Unlabelled: The purpose of this study was to explore the feasibility of (11)C-choline in the assessment of the degree of inflammation in atherosclerotic plaques.

Methods: Uptake of (11)C-choline was studied ex vivo in tissue samples and aortic sections excised from 6 atherosclerotic mice deficient for both low-density lipoprotein receptor and apolipoprotein B48 (LDLR(-/-)ApoB(100/100)) and 5 control mice. The autoradiographs were compared with the immunohistology of the arterial sites.

Results: The uptake of (11)C-choline (percentage of the injected activity per gram of tissue) in the atherosclerotic aortas of the LDLR(-/-)ApoB(100/100) mice was significantly higher (1.9-fold, P = 0.0016) than that in the aortas of the control mice. The autoradiography analysis showed significantly higher uptake of (11)C-choline in the plaques than in healthy vessel wall (mean ratio, 2.3 +/- 0.6; P = 0.014), prominently in inflamed plaques, compared with noninflamed plaque areas.

Conclusion: We observed a high (11)C-choline uptake in the aortic plaques of atherosclerotic mice. Our data suggest that macrophages may be responsible for the uptake of (11)C-choline in the plaques.
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http://dx.doi.org/10.2967/jnumed.109.071704DOI Listing
May 2010

Comparison of 2beta-carbomethoxy-3beta-(4-[18F]fluorophenyl)tropane and N-(3-[18F]fluoropropyl)-2beta-carbomethoxy-3beta-(4-fluorophenyl)nortropane, tracers for imaging dopamine transporter in rat.

Mol Imaging Biol 2010 Jun 1;12(3):269-77. Epub 2009 Dec 1.

MediCity/PET Preclinical Laboratory, Turku PET Centre, University of Turku, Tykistökatu 6A, FI-20520, Turku, Finland.

Purpose: This study compares 2beta-carbomethoxy-3beta-(4-[(18)F]fluorophenyl)tropane ([(18)F]beta-CFT) and N-(3-[(18)F]fluoropropyl)-2beta-carbomethoxy-3beta-(4-fluorophenyl)nortropane ([(18)F]beta-CFT-FP) as radiotracers for imaging the dopamine transporter (DAT) in rat.

Procedures: Biodistribution, specificity and selectivity of the radiotracers were studied ex vivo in rats pre-treated with specific antagonists for DAT, serotonin transporter (SERT) and noradrenalin transporter (NET) and in control rats. Positron emission tomography (PET) studies were performed using an HRRT scanner. Radiolabelled metabolites were analyzed with thin-layer chromatography.

Results: [(18)F]beta-CFT showed slow kinetics with a maximum striatum/cerebellum uptake ratio of 9.2 at 120 min. [(18)F]beta-CFT-FP showed fast kinetics with a maximum ratio of 3.1 at 5 min. Both tracers bound to DAT. [(18)F]beta-CFT also bound to NET. [(18)F]beta-CFT was more resistant to metabolism than [(18)F]beta-CFT-FP.

Conclusions: Structural modifications of [(18)F]beta-CFT significantly changed its biological properties, as shown by [(18)F]beta-CFT-FP. [(18)F]beta-CFT is a suitable tracer for both preclinical and human PET studies, but [(18)F]beta-CFT-FP is less suitable as a PET tracer.
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http://dx.doi.org/10.1007/s11307-009-0278-0DOI Listing
June 2010

Extracellular superoxide dismutase is a growth regulatory mediator of tissue injury recovery.

Mol Ther 2009 Mar 23;17(3):448-54. Epub 2008 Dec 23.

Medicity Research Laboratory, University of Turku, Turku, Finland.

Extracellular superoxide dismutase (SOD3) gene therapy has been shown to attenuate tissue damages and to improve the recovery of the tissue injuries, but the cellular events delivering the therapeutic response of the enzyme are not well defined. In the current work, we overexpressed SOD3 in rat hindlimb ischemia model to study the signal transduction and injury healing following the sod3 gene transfer. The data suggest a novel sod3 gene transfer-derived signal transduction cascade through Ras-Mek-Erk mitogenic pathway leading to activation of AP1 and CRE transcription factors, increased vascular endothelial growth factor (VEGF)-A and cyclin D1 expression, increased cell proliferation, and consequently improved metabolic functionality of the injured tissue. Increased cell proliferation could explain the improved metabolic performance and the healing of the tissue damages after the sod3 gene transfer. The present data is a novel description of the molecular mechanism of SOD3-mediated recovery of tissue injury and suggests a new physiological role for SOD3 as a Ras regulatory molecule in signal transduction.
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http://dx.doi.org/10.1038/mt.2008.282DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835086PMC
March 2009

Uptake of inflammatory cell marker [11C]PK11195 into mouse atherosclerotic plaques.

Eur J Nucl Med Mol Imaging 2009 Jan 19;36(1):73-80. Epub 2008 Aug 19.

Turku PET Centre, University of Turku, Kiinamyllynkatu 4-8, FI-20520, Turku, Finland.

Purpose: The ligand [(11)C]PK11195 binds with high affinity and selectivity to peripheral benzodiazepine receptor, expressed in high amounts in macrophages. In humans, [(11)C]PK11195 has been used successfully for the in vivo imaging of inflammatory processes of brain tissue. The purpose of this study was to explore the feasibility of [(11)C]PK11195 in imaging inflammation in the atherosclerotic plaques.

Methods: The presence of PK11195 binding sites in the atherosclerotic plaques was verified by examining the in vitro binding of [(3)H]PK11195 onto mouse aortic sections. Uptake of intravenously administered [(11)C]PK11195 was studied ex vivo in excised tissue samples and aortic sections of a LDLR/ApoB48 atherosclerotic mice. Accumulation of the tracer was compared between the atherosclerotic plaques and non-atherosclerotic arterial sites by autoradiography and histological analyses.

Results: The [(3)H]PK11195 was found to bind to both the atherosclerotic plaques and the healthy wall. The autoradiography analysis revealed that the uptake of [(11)C]PK11195 to inflamed regions in plaques was more prominent (p = 0.011) than to non-inflamed plaque regions, but overall it was not higher than the uptake to the healthy vessel wall. Also, the accumulation of (11)C radioactivity into the aorta of the atherosclerotic mice was not increased compared to the healthy control mice.

Conclusions: Our results indicate that the uptake of [(11)C]PK11195 is higher in inflamed atherosclerotic plaques containing a large number of inflammatory cells than in the non-inflamed plaques. However, the tracer uptake to other structures of the artery wall was also prominent and may limit the use of [(11)C]PK11195 in clinical imaging of atherosclerotic plaques.
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http://dx.doi.org/10.1007/s00259-008-0919-6DOI Listing
January 2009

Ex vivo evaluation of N-(3-[18F]fluoropropyl)-2 beta-carbomethoxy-3 beta-(4-fluorophenyl)nortropane in rats.

Nucl Med Biol 2008 Feb;35(2):177-83

Laboratory of Radiochemistry, Department of Chemistry, University of Helsinki, PO Box 55, FI-00014 Helsinki, Finland.

Introduction: The dopamine transporter (DAT) ligand N-(3-fluoropropyl)-2 beta-carbomethoxy-3beta-(4-fluorophenyl)nortropane (beta-CFT-FP) was labeled with fluorine-18, and its biodistribution was evaluated in rats ex vivo.

Methods: The distribution of 18F radioactivity in the brain and peripheral organs and tissues was determined at several time points 5-120 min after intravenous injection of [18F]beta-CFT-FP.

Results: The highest brain uptake of [18F]beta-CFT-FP was localized in the striatum; limbic structures also exhibited high uptake. Low uptake was found in the cerebellum. The highest ratio of striatum-to-cerebellum uptake, already reached within 5 min, was 3.1. Pretreatment with the selective DAT inhibitor GBR12909 significantly decreased [18F]beta-CFT-FP uptake in the striatum. In most peripheral tissues, the highest uptake was found at 5 min, indicating fast washout of the radioligand. Some accumulation of (18)F radioactivity was seen in bone as a function of time, reflecting defluorination of the radioligand.

Conclusion: The results indicate that [18F]beta-CFT-FP is a potential radioligand for studying DAT in vivo with positron emission tomography.
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http://dx.doi.org/10.1016/j.nucmedbio.2007.09.006DOI Listing
February 2008