Targeting activated microglia in Alzheimer's pathology by intraventricular delivery of a phagocytosable MRI contrast agent in APP23 transgenic mice

The role of phagocytosing immune cells in Alzheimer's pathology can be studied experimentally in APP23 transgenic mice. This present study intended to label phagocytosing immune cells in the plaque periphery of APP23 mice in vivo by intraventricular injection of VSOP-C184, a phagocytosable iron oxide nanoparticle MRI contrast agent. Firstly, the dosages of 0.1, 1.0 and 10 mu mol Fe/kg body weight dissolved in 500 nl of artificial cerebrospinal fluid, delivered by stereotaxic surgery were evaluated 4 h after surgery in 7 wild type mice using 7 T MRI. Secondly, the dosage of 10 mu mol Fe/kg body weight was investigated in 6 APP23 mice. The distribution of iron oxide particles was evaluated histologically. The injection of 0.1 mu mol Fe/kg body weight did not result in any signal alterations, 10 mu mol resulted in strong signal artifacts. The delivery of 1.0 mu mol Fe/ kg body weight in wild type mice resulted in MRI signal alterations throughout the ventricular system without large artifacts. It was regarded superior to other dosages for the study of the transgenic mice. There was no difference in MRI signal alterations and the distribution of iron particles in the histology between APP23 and wild type mice using the dosage of 1.0 mu mol Fe/ kg body weight. Upon intraventricular injection, the phagocytosable contrast agent VSOP-C184 distributes throughout the ventricular system, whereas it does not reach the periphery of amyloid plaques in APP23 mice in a concentration sufficient to cause MRI signal alterations. (C) 2009 Elsevier Inc. All rights reserved.