An in vivo Pig Model for Testing Novel Positron Emission Tomography Radioligands Targeting Cerebral Protein Aggregates

Nakul Ravi Raval; Arafat Nasser; Clara Aabye Madsen; Natalie Beschorner; Emily Eufaula Beaman; Morten Juhl; Szabolcs Lehel; Mikael Palner; Claus Svarer; Pontus Plavén-Sigray; Louise Møller Jørgensen; Gitte Moos Knudsen

doi:10.3389/fnins.2022.847074

An in vivo Pig Model for Testing Novel Positron Emission Tomography Radioligands Targeting Cerebral Protein Aggregates

Front Neurosci. 2022 Mar 16:16:847074. doi: 10.3389/fnins.2022.847074. eCollection 2022.

Authors

Nakul Ravi Raval^{1

2}, Arafat Nasser¹, Clara Aabye Madsen^{1

2}, Natalie Beschorner³, Emily Eufaula Beaman¹, Morten Juhl⁴, Szabolcs Lehel⁵, Mikael Palner^{1

6

7}, Claus Svarer¹, Pontus Plavén-Sigray¹, Louise Møller Jørgensen^{1

2

8}, Gitte Moos Knudsen^{1

2}

Affiliations

¹ Neurobiology Research Unit, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
² Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
³ Center for Translational Neuromedicine, University of Copenhagen, Copenhagen, Denmark.
⁴ Cardiology Stem Cell Centre, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
⁵ Department of Clinical Physiology, Nuclear Medicine and Positron Emission Tomography (PET), Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
⁶ Department of Clinical Research, Clinical Physiology and Nuclear Medicine, University of Southern Denmark, Odense, Denmark.
⁷ Department of Nuclear Medicine, Odense University Hospital, Odense, Denmark.
⁸ Copenhagen Spine Research Unit, Copenhagen University Hospital (Rigshospitalet), Glostrup, Denmark.

Abstract

Positron emission tomography (PET) has become an essential clinical tool for diagnosing neurodegenerative diseases with abnormal accumulation of proteins like amyloid-β or tau. Despite many attempts, it has not been possible to develop an appropriate radioligand for imaging aggregated α-synuclein in the brain for diagnosing, e.g., Parkinson's Disease. Access to a large animal model with α-synuclein pathology would critically enable a more translationally appropriate evaluation of novel radioligands. We here establish a pig model with cerebral injections of α-synuclein preformed fibrils or brain homogenate from postmortem human brain tissue from individuals with Alzheimer's disease (AD) or dementia with Lewy body (DLB) into the pig's brain, using minimally invasive surgery and validated against saline injections. In the absence of a suitable α-synuclein radioligand, we validated the model with the unselective amyloid-β tracer [¹¹C]PIB, which has a high affinity for β-sheet structures in aggregates. Gadolinium-enhanced MRI confirmed that the blood-brain barrier was intact. A few hours post-injection, pigs were PET scanned with [¹¹C]PIB. Quantification was done with Logan invasive graphical analysis and simplified reference tissue model 2 using the occipital cortex as a reference region. After the scan, we retrieved the brains to confirm successful injection using autoradiography and immunohistochemistry. We found four times higher [¹¹C]PIB uptake in AD-homogenate-injected regions and two times higher uptake in regions injected with α-synuclein-preformed-fibrils compared to saline. The [¹¹C]PIB uptake was the same in non-injected (occipital cortex, cerebellum) and injected (DLB-homogenate, saline) regions. With its large brain and ability to undergo repeated PET scans as well as neurosurgical procedures, the pig provides a robust, cost-effective, and good translational model for assessment of novel radioligands including, but not limited to, proteinopathies.

Keywords: PET; PiB - Pittsburgh compound B; alpha-synucein; amyloid-β; large animal PET; pig brain imaging; pig model; protein injection model.