Detection of Amyloid Plaques Targeted by Bifunctional USPIO in Alzheimer’s Disease Transgenic Mice Using Magnetic Resonance Microimaging

Youssef Zaim Wadghiri,Jialin Li,Hong Xu,Andrew Wang,Dung Minh Hoang,Allal Boutajangout,Jinhuan Wang,Yanjie Sun,Yongsheng Li,Wai Tsui,Thomas Wisniewski,Mony De Leon,Taisuke Tomita

doi:10.1371/journal.pone.0057097

Abstract

Amyloid plaques are a key pathological hallmark of Alzheimer’s disease (AD). The detection of amyloid plaques in the brain is important for the diagnosis of AD, as well as for following potential amyloid targeting therapeutic interventions. Our group has developed several contrast agents to detect amyloid plaques in vivo using magnetic resonance microimaging (µMRI) in AD transgenic mice, where we used mannitol to enhance blood brain barrier (BBB) permeability. In the present study, we used bifunctional ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, chemically coupled with Aβ1-42 peptide to image amyloid plaque deposition in the mouse brain. We coupled the nanoparticles to polyethylene glycol (PEG) in order to improve BBB permeability. These USPIO-PEG-Aβ1-42 nanoparticles were injected intravenously in AD model transgenic mice followed by initial in vivo and subsequent ex vivo μMRI. A 3D gradient multi-echo sequence was used for imaging with a 100 µm isotropic resolution. The amyloid plaques detected by T2*-weighted μMRI were confirmed with matched histological sections. The region of interest-based quantitative measurement of T2* values obtained from the in vivo μMRI showed contrast injected AD Tg mice had significantly reduced T2* values compared to wild-type mice. In addition, the ex vivo scans were examined with voxel-based analysis (VBA) using statistical parametric mapping (SPM) for comparison of USPIO-PEG-Aβ1-42 injected AD transgenic and USPIO alone injected AD transgenic mice. The regional differences seen by VBA in the USPIO-PEG-Aβ1-42 injected AD transgenic correlated with the amyloid plaque distribution histologically. Our results indicate that USPIO-PEG-Aβ1-42 can be used for amyloid plaque detection in vivo by intravenous injection without the need to co-inject an agent which increases permeability of the BBB. This technique could aid the development of novel amyloid targeting drugs by allowing therapeutic effects to be followed longitudinally in model AD mice.

Highlights

The extracellular accumulations of amyloid b (Ab) peptides as plaques and cerebral amyloid angiopathy (CAA), as well as intracellular neurofibrillary tangles (NFTs) are pathological hallmarks of Alzheimer’s disease (AD) [1]
Our studies report the ability of bi-functional ultrasmall superparamagnetic iron oxide (USPIO) coupled to both polyethylene glycol (PEG) and Ab1-42 to cross the blood brain barrier (BBB) and target amyloid deposits following intravenous femoral injections
In our prior studies we have used an intra-carotid or an intravenous route with a requirement for co-injections of mannitol to disrupt the BBB [13,19,26,27]. This is a well studied and effective means of increasing the permeability of the BBB, allowing the CNS delivery of various agents such as neurotrophic factors, viral vectors and USPIO [49,50,51], it has a short duration of action (,15 min in rodents) [50] and it is associated with some toxicity

Summary

Introduction

The extracellular accumulations of amyloid b (Ab) peptides as plaques and cerebral amyloid angiopathy (CAA), as well as intracellular neurofibrillary tangles (NFTs) are pathological hallmarks of Alzheimer’s disease (AD) [1]. We tried to increase the BBB permeability of the ligand by incorporation of polylysine residues (K6) on Ab, with the use of K6-Ab-Gd-DPTA [18] This improved plaque visualization; we still needed to inject the ligand by ic injection with mannitol to allow passage across the BBB. The strong darkening effects exhibited by these particles on T2 and T2* imaging sequences gives a greater contrast to noise ratio and allows a smaller dose of ligand to be used This technique still requires femoral co-injection of mannitol for CNS imaging as USPIO do not cross the intact BBB. In the current study we have produced bi-functional USPIO particles coupled to both Ab1-42 and PEG, in order to assess their utility to visualize amyloid plaques in vivo using AD model transgenic mice following intravenous injection, without the co-injection of an agent to increase permeability of the BBB

Methods

Results

Conclusion