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Evaluation of  PET tracers [11C]D-deprenyl, [11C]L-dideuteriumdeprenyl and [18F]FDG for Visualization of Acute Inflammation in a Rat Model of Pain - Preliminary Findings.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Preclinical PET Platform.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Preclinical PET Platform.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Purpose: Positron emission tomography with the radioligand [11C]D-deprenyl has shown an increased signal at the location of pain in patients with ankle sprains, rheumatoid arthritis and chronic whiplash injury, but the mechanism of this tracer uptake and its exact binding site in inflammation or tissue injury is still unclear. The aim of this study was to further evaluate [11C]D-deprenyl´s usefulness as a marker of acute inflammation.

Methods: An animal PET/CT study was performed three days after the induction of a rat model of inflammatory or surgical pain. Fourteen adult male Sprague-Dawley rats and three tracers [11C]D-deprenyl, [11C]L-dideuterumdeprenyl and [18F]fluorodeoxyglucose were used.

Results: No [11C]D-deprenyl accumulation was seen in a rat model of musculoskeletal pain. In the rat model of inflammatory pain all three ligands were shown to visualize the inflamed ankle joint with much lower uptake in the control ankle joint. The uptake was largest with [11C]D-deprenyl and [11C]L- dideuteriumdeprenyl, where approximately 1 % of the injected dose could be found in the affected ankle joint during the first minutes, whereas the uptake of [18F]FDG was approximately 0.5 % of the injected dose. However, the ratio of uptake of the injected ankle joint versus the control ankle joint was much higher for [18F]FDG (around 10 fold increase) than for the two deprenyl enantiomers (2 – 3 fold increase). The uptake pattern of [11C]D-deprenyl and [11C]L-dideuteriumdeprenyl did not show signs of specific binding or irreversible trapping.

Conclusions: Contrary to our expectations, of the three tracers only [18F]FDG may be used as markers of peripheral inflammation in a rat model of inflammatory pain. However, as a high site-specificity is required, [11C]D-deprenyl and [11C]L-dideyteriumdeprenyl deserve further exploration regarding sensitivity, specificity and uptake mechanisms in human pain syndromes.

Keywords [en]
deprenyl; inflammation; pain; PET; carbon-11
National Category
Medical and Health Sciences
Research subject
Anaesthesiology and Intensive Care
Identifiers
URN: urn:nbn:se:uu:diva-347604OAI: oai:DiVA.org:uu-347604DiVA, id: diva2:1195305
Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-12
In thesis
1. Visualization of Peripheral Pain Generating Processes and Inflammation in Musculoskeletal Tissue using [11C]-D-deprenyl PET
Open this publication in new window or tab >>Visualization of Peripheral Pain Generating Processes and Inflammation in Musculoskeletal Tissue using [11C]-D-deprenyl PET
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

An objective visualization and quantification of pain-generating processes in the periphery would alter pain diagnosis and represent an important paradigm shift in pain research. Positron emission tomography (PET) radioligand [11C]-D-deprenyl has shown an elevated uptake in painful inflammatory arthritis and whiplash-associated disorder. However, D-Deprenyl’s molecular binding target and uptake mechanism in inflammation and musculoskeletal injuries are still unknown. The present thesis aimed to gain insight into the mechanisms of D-deprenyl binding and uptake and to verify whether pain-associated sites and inflammation in acute musculoskeletal injury could be visualized, objectively quantified and followed over time with [11C]-D-deprenyl PET-computed tomography (PET/CT).

To identify the D-deprenyl binding target, a high-throughput analysis and competitive radioligand binding studies were performed. D-deprenyl inhibited monoamine oxidase A (MAO-A) activity by 55%, MAO-B activity by 99% and angiotensin-converting enzyme (ACE) by 70%, which identified these enzymes as higher-affinity targets. Furthermore, radioligand receptor binding assays pointed favorably towards the concept of MAO-B as the primary target. To investigate the biochemical characteristics of the binding site, we used radioligand binding assays to assess differences in the binding profile in inflamed human synovial membranes exhibiting varying levels of inflammation. D-deprenyl bound to a single, saturable population of membrane-bound protein in synovial membrane homogenates and the level of inflammation correlated with an increase in D-deprenyl binding affinity.

To verify whether D-deprenyl can visualize pain-generating processes, patients with musculoskeletal injuries were investigated and followed-up with [11C]-D-deprenyl PET/CT. In the study of eight patients with ankle sprain, the molecular aspects of inflammation and tissue injury could be visualized, objectively quantified and followed over time with [11C]-D-deprenyl PET/CT. The pain coexisted with increased [11C]-D-deprenyl uptake. In the study of 16 whiplash patients, an altered [11C]-D-deprenyl uptake in the cervical bone structures and facet joints was associated with subjective pain levels and self-rated disability.

To further evaluate D-Deprenyl’s usefulness as a marker of inflammation, three PET tracers were compared in an animal PET/CT study. Preliminary findings showed that [11C]-D-deprenyl had an almost identical uptake pattern when compared with [11C]-L-deprenyl. The two deprenyl enantiomers showed no signs of specific binding or trapping and therefore may not be useful to study further in models of inflammatory pain, surgical pain, or both.

This thesis demonstrates that D-deprenyl visualizes painful inflammation in musculoskeletal injuries and that the probable underlying mechanism of [11C]-D-deprenyl uptake is binding to MAO.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 72
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1456
Keywords
ankle injuries, arthritis, binding site, binding target, carbon-11, deprenyl, high-throughput screening, inflammation, monoamine oxi-dase, pain, PET, whiplash
National Category
Anesthesiology and Intensive Care Radiology, Nuclear Medicine and Medical Imaging
Research subject
Anaesthesiology and Intensive Care
Identifiers
urn:nbn:se:uu:diva-347685 (URN)978-91-513-0313-0 (ISBN)
Public defence
2018-05-25, Universitetshuset, Biskopsgatan 3, Uppsala, 09:00 (Swedish)
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Supervisors
Available from: 2018-05-02 Created: 2018-04-06 Last updated: 2018-10-08

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