Brain Advance Access originally published online on March 17, 2009
Brain 2009 132(5):1346-1354; doi:10.1093/brain/awp031
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Clinical field-strength MRI of amyloid plaques induced by low-level cholesterol feeding in rabbits
1 Robarts Research Institute, University of Western Ontario, London, ON, Canada 2 Department of Medical Biophysics, University of Western Ontario, London, ON, Canada 3 Department of Diagnostic Radiology and Nuclear Medicine, University of Western Ontario, London, ON, Canada 4 Department of Anatomy and Cell Biology, University of Western Ontario, London, ON, Canada 5 Department of Radiology, Stanford University, Palo Alto, California, USA
Correspondence to: John A. Ronald, Robarts Research Institute, University of Western Ontario, 100 Perth Drive, 1st Floor, London, ON, Canada N6A 5K8 E-mail: jronald{at}imaging.robarts.ca
Two significant barriers have limited the development of effective treatment of Alzheimer's disease. First, for many cases the aetiology is unknown and likely multi-factorial. Among these factors, hypercholesterolemia is a known risk predictor and has been linked to the formation of β-amyloid plaques, a pathological hallmark this disease. Second, standardized diagnostic tools are unable to definitively diagnose this disease prior to death; hence new diagnostic tools are urgently needed. Magnetic resonance imaging (MRI) using high field-strength scanners has shown promise for direct visualization of β-amyloid plaques, allowing in vivo longitudinal tracking of disease progression in mouse models. Here, we present a new rabbit model for studying the relationship between cholesterol and Alzheimer's disease development and new tools for direct visualization of β-amyloid plaques using clinical field-strength MRI. New Zealand white rabbits were fed either a low-level (0.125–0.25% w/w) cholesterol diet (n = 5) or normal chow (n = 4) for 27 months. High-resolution (66 x 66 x 100 µm3; scan time = 96 min) ex vivo MRI of brains was performed using a 3-Tesla (T) MR scanner interfaced with customized gradient and radiofrequency coils. β-Amyloid-42 immunostaining and Prussian blue iron staining were performed on brain sections and MR and histological images were manually registered. MRI revealed distinct signal voids throughout the brains of cholesterol-fed rabbits, whereas minimal voids were seen in control rabbit brains. These voids corresponded directly to small clusters of extracellular β-amyloid-positive plaques, which were consistently identified as iron-loaded (the presumed source of MR contrast). Plaques were typically located in the hippocampus, parahippocampal gyrus, striatum, hypothalamus and thalamus. Quantitative analysis of the number of histologically positive β-amyloid plaques (P < 0.0001) and MR-positive signal voids (P < 0.05) found in cholesterol-fed and control rabbit brains corroborated our qualitative observations. In conclusion, long-term, low-level cholesterol feeding was sufficient to promote the formation of extracellular β-amyloid plaque formation in rabbits, supporting the integral role of cholesterol in the aetiology of Alzheimer's disease. We also present the first evidence that MRI is capable of detecting iron-associated β-amyloid plaques in a rabbit model of Alzheimer's disease and have advanced the sensitivity of MRI for plaque detection to a new level, allowing clinical field-strength scanners to be employed. We believe extension of these technologies to an in vivo setting in rabbits is feasible and that our results support future work exploring the role of MRI as a leading imaging tool for this debilitating and life-threatening disease.
Key Words: Alzheimer's disease; cholesterol; rabbit model; magnetic resonance imaging; β-amyloid plaques
Abbreviations: 3DFIESTA, three-dimensional fast imaging employing steady state acquisition; ANOVA, analysis of variance; MRI, magnetic resonance imaging; SNR, signal-to-noise ratio; T, Tesla
Received September 30, 2008. Revised January 19, 2009. Accepted January 22, 2009.